This comes up once every couple of year, and I think it's best that we re-evaluate it from time to time to see if having the GPL available as an option still meets the needs of the community.

The reason the GPL is a license option at all is because there were several major projects that, at the time of OGA's creation, required their art to be licensed under the GPL (Wesnoth comes to mind, although I believe there were others), and because of the existence of legacy works from back when the GPL was the only game in town as far as licenses with a "share-alike" requirement.

The GPL isn't really a very good art license, because what constitutes the "source" for a particular piece of art is often ill-defined.  The main example I can think of is a recording of improvised music.  If you're improvising a musical work, there's no musical score to speak of, and the artist doesn't have a responsibility to generate one just because they happen to want to license their work under the GPL.  In fact, generally, it applies poorly to any work of art that doesn't start out as a digital work.  A scanned acrylic painting would be another example of this, since the "source" is the physical original (since no scanning process is ever going to reproduce the work with perfect fidelity). 

Another rather fuzzy example is art generated in (for instance) Photoshop.  Ideally, the source file would be the PSD, but Photoshop itself is proprietary (and expansive), and other programs that try to open Photoshop files (The GIMP, for instance) often don't quite get it right.  If you have photoshop, the preferred form of the work for modification would be the PSD; otherwise, it would probably be a PNG file of each layer.

In conclusion, I don't think it's particularly clear-cut whether the source requirement can always apply to any form of media, not just music, and my preference is that we allow the artist to be responsible for making this determination.

So, let's talk about this.  I'd like to get input from the community on what we should do with current GPLed art works, and whether or not we should continue allowing artists to select the GPL as a license for their work. Since these discussions can get sidetracked pretty easily, I'd like to ask in advance that people refrain from discussion two things in this thread:

• Licenses other than the GPL
• Opinions about how copyright law, licensing, and/or the GPL ought to work (as opposed to how it does work)

I'll open this thread up for comments and close it once we get to the point that no significant amount of new information is being posted (that is, either nothing is being posted at all, or we're stuck in a loop and rehashing the same arguments over and over).  Please understand that not everyone is going to agree on the outcome, and that I'm going to have to reach some sort of decision about this, even if that decision is to leave things exactly as they are.

My view is that the GPL is a complicated license clearly designed for software and is difficult to understand and use for any other kind of media.  Heck, sometimes it is difficult to use even for software.  Plenty of projects have gotten into rules lawyering arguments about the functioning legal definition of a derivative work, how different contributors' inputs combine, whether certain combinations are "aggregations" or "derivations", the "preferred" form of modification, what the patent provisions of GPL 3 require and are actually supposed to do, and several other issues.

I don't use or collect any art which is GPL-only due to the non-trivial chance of a dispute over these and other provisions in the GPL.  One thing to note is that CC BY-SA has a lesser concern of a similar nature where various parties don't agree on if or when source code actually combines with multimedia elements that it is processing at runtime.  Thus, the safest path is to leave out any BY-SA assets from projects that you can't be sure will be open source at release.

Having evaluated and built a personal curated collection of works from this site, honestly I'd have to say that most of the best work is already available under CC0, CC-BY, or OGA-BY (with a few notable BY-SA exceptions).  By far the biggest thing missing is the core LPC assets that are BY-SA & GPL only.  Although even then, some of the extensions/expansions/modifications are under more liberal terms.

As to the specific question of what the "preferred" modification form would be understood to mean in an actual court of law, my guess is that it's likely to be whatever the artist would have actually used in the production of the asset.  So if you compose and instrument your song with LMMS, for instance, the LMMS project file and any external resources it requires would become the preferred form.  Likewise, an image made with GIMP would need to ship the XCF file.  As Bart points out, though, this becomes a significant practical issue with proprietary software.  It might be impossible to actually edit the "source" file without that particular piece of software, or worse, that software plus a bunch of external proprietary modules, too.  This is naturally a good reason to avoid closed formats.

 Ok, I am going to try again as new post, just to see if that helps with the formatting...

I don't think it's useful to argue about what constitutes the 'preferred format of modification' for the various artworks on OGA.

Unless there's a golden table somewhere that specifies exactly what constitutes the 'preferred format' for every type of work, it's a moot point, you can't win the argument one way or the other.

As an example, gsliepen sites music stored as an .ogg as an non-preffered format.  

As a developer, I can say that is exactly my preferred format for modifying game music.  It's well compressed and it's a common file format.  I can quickly and easily load it into an editor of my choice and make the modifications I'd want to make (most likely re-leveling the volume and some alight eq adjustments to make it match the rest of the game audio, plus probably slice a few bars off the front to make the song start faster).  For me this is infinitely preferable to a MIDI or whatever file meant to be loaded into some music creation application I don't own or don't have installed on my PC.

So you see, you can argue the 'preferred format' from here to Eternia, unless you want to make a judge decide, there's no winning that one. 

At the end of the day, you just have to take it on good faith that the artist has provided the work in the format they thought was 'preferred'.

Anyway, do we think some people are disingenuously posting works here as GPL while deliberately withholding the 'preferred format' source files?   

Is OGA trying to make a mockery out of GPL by intentionally hosting works without source in 'the preferred form for modifications'?

No, of course not.  Works are posted and hosted in the formats that submitters think would be most useful to others.  

If you want the work in another format all you have to do is ask.  You see requests like that all the time on here and artists generally oblige.  And if they don't, it's typically because they literally can't, as in 'I found these .wavs on an old hard drive, they were part of an old project and unfortunately I've lost the .xyz files I used to make them'. 

@bart: re: including GPL among the licenses, I don't support removing it (the original reasons for including it still seem valid to me) but I do support burying it a bit on the submission form and surrounding it with flashing neon lights that say 'don't click here unless you are absolutely sure you know what you are doing!!'

I don't upload the component editing files for most of my art primarily because the size is often many orders of magnitude larger than the mixed down final form.  An ogg which is 3mb could easily be exported from a set of source files which is several gigabytes in size. Even that is not always the whole source, I might make 15 or 20 different iterations of an artwork prior to settling on a final form, I save each of those versions as a seperate project, and I can extract components from multiple versions to use in the final version.  At that point you're potentially looking at dozens of gigabytes of "source" files.

Hell, for most of the songs on here I have also made video clips, which also have multiple versions and massive source files.  If I were to upload all of that information, I would be seeding for months.  These editing component files are very unlikely to be used by a game dev, and would have a significant effect on the hosting cost of the site. There are a lot of downsides to uploading source files rather than the final mix.  

For all the discussion in this thread, I still don't see what the problem is with simply asking an artist for a different fomat if you need it. 

GPL v3 section 6b and 6c:

• b) Convey the object code in, or embodied in, a physical product (including a physical distribution medium), accompanied by a written offer, valid for at least three years and valid for as long as you offer spare parts or customer support for that product model, to give anyone who possesses the object code either (1) a copy of the Corresponding Source for all the software in the product that is covered by this License, on a durable physical medium customarily used for software interchange, for a price no more than your reasonable cost of physically performing this conveying of source, or (2) access to copy the Corresponding Source from a network server at no charge.
• c) Convey individual copies of the object code with a copy of the written offer to provide the Corresponding Source. This alternative is allowed only occasionally and noncommercially, and only if you received the object code with such an offer, in accord with subsection 6b.

It seems like keeping GPL is fine, as long as the artist explicitly agrees to offer a copy of the source for at least three years. At that point the artist would be meeting b) and OGA would be meeting c) 

Well, I've downloaded plenty of linux distros in my time and I've never once come across a folder full of layered PSD or XCF files representing the 'source' for all the various images, wallpapers, logos, icons, etc. etc. that came with the distro.   Nor have I ever seen similar for the miscellaneous sound files that come with a distro.

It's not like source code where there's a set of common well defined 'preferred formats'.

The works are provided in the format people find useful.  

If you want something in another format, ask.  Under GPL, source only has to be provided upon request anyways, so make tbe request.  

@gsliepen How can you say "it doesn't work like that"?   The ogg version of a song is equivilant to the "object code" in the GPL licence, as it is the final compiled version without the actual "source code".  

Section 4 says "You may convey verbatim copies of the Program's source code as you receive it" 

And section 6 says "You may convey a covered work in object code form under the terms of sections 4"  

with the provisos of section 6c  "Convey individual copies of the object code with a copy of the written offer to provide the Corresponding Source" 

So if the artist agreed to provide the source on request then OGA would be conveying a verbatim copy of the object code with a verbatim copy of a written offer to provide the corresponding source.  

gsliepen, I think you're substantially overestimating the number of "GPL-only" works on the site.  The license search function is an MATCH ANY search, not an ONLY or AND search.  Thus, when you select GPL you get works with GPL available, but they very rarely have only that (in my experience of browsing thousands of entries).  Typically, BY-SA or BY is marked as an alternative license.

Presumably the idea from the creator(s) is that they wanted it to be possible to integrate their work into GPL games, so they checked off the box in passing.  My legal understanding of the prevailing theory from FSF and elsewhere is that the art doesn't actually need to be GPL in order to be included and used by GPL software without issue.

 The problem is you can't say what the preferred format is, only what format you'd prefer.  So you can't really claim someone hasn't provided 'source' already.    Anyway, it's a choice, OGA can host GPL works and let folks request something in an alternate format if they think it'd be useful for them, or OGA can remove all GPL'd works and revel in it's purity. I for one am ok with the former. I will add that I am on record saying that ALL the licenses on this site need better explaining and GPL in particular needs some serious caveats around it to discourage the sort of accidental licensing ya'll deacribe. http://opengameart.org/forumtopic/site-faqsubmission-guidelines-updatesc... 

I've always interpreted the "preferred format" as the format preferred by the IP owner, in this case, the artist. It may not be the best format for editing, but I beleive the purpose of that statement (at least in part) is to disuade 2nd parties (not the original artist) from taking, say, a png file that's released as GPL and converting it to an overly compressed jpeg, adding a water mark, then redistributing that version of the image to try to satisfy the GPL. GPL's like "nah, dude. That isn't the artist's preferred format."

"That's a dangerous attitude. Also, don't forget that it is not just OGA which might get into trouble for not being able to provide the source for works under the GPL, it's also those who download GPL'ed assets for use in their own works that end up having to bear this burden. The whole point of going to OGA instead of most other "free" image/sound/music sites is that we can be sure that things are properly licensed here."

The thing that sets OGA apart from other foss sites is not so much the guarantee of proper licensing (although that is present) It is the attitude of honoring artists wishes even when the license allows things the artist does not wish. A guarantee of being technically compliant with a license is not what we're about. Only the copyright holder (artist) can claim a greivance on a potential infringement of their works. If the copyright holder only provided an mp3 file, why would they claim greivance against OGA or anyone else for failing to provide the "source" when they themselves haven't provided what they consider the source? Who is going to get anyone "in trouble"? I can't sue capbros for distributing bart's work, especially when bart has given capbros his blessing. This isn't just technically allowed, it's also adhereing to the artist's implicit wishes.

Should artists provide GPL artwork in an easily adaptable format? Absolutely. Can they? not always. Must they? I don't think so. Asking artists for flexible formats is great, but demanding they do so is taking a decent license and twisting it into a bureaucratic mess.

@MedicineStorm:   Well put all the way around.

@gsliepen:  Sorry if I've come off as contentious here, I guess I can be a bit defensive on OGA's behalf at times.    But I want to say, you have an important issue and one well worth discussing.  And I totally get the point you are making, if this were a site full of binaries for GPL'd programs with no source code in site, that would be a scandal.  I think the point the rest of us are making is that with art works it isn't nearly so clear cut and OGA has chosen to be flexible rather than rigid on the issue.

Let me add that I only wish I were good enough to use bart's art in my projects!

"The problem is that when you upload something to OGA that has the GPL license, then OGA itself becomes a distributor of the GPL'ed work. Legally, the burden is then on OGA to provide the sources on request, as required by the GPL."

Just a quick side-note here, that's not necessarily the case.  If the author uploads their own work here OGA is hosting it with their direct permission, not under the terms of the GPL.  That it happens to be GPL-licensed is irrelevant.  I'm not sure whether there's a similar out in the case of people who aren't the sole author of a work uploading though.

My statement about only copyright holders being able to claim greivances is not an assumption. I can't give any official legal advice, and obviously each legal situation is unique and not subject to generalization, but I'll just say I'm very confident of this. Only the artist (a stakeholder in the copyright) can sue you for infringement of their work.

They would be ridiculous to sue you for not distributing source they didn't provide. That may be an assumption, but cautioning against it is a bit like saying "Don't assume your neighbor will not sue you for borrowing the hammer that he never had." :)

I think RedShrike is mistaken, the works on OGA are most definitely distributed under terms of the chosen licenses and not by any special agreement between an artist and OGA.   Aside from glsiepen's point that no such secondary agreement is ever presented to submitters, also consider the fact that OGA accepts third party submissions where there is no chance for such an agreement between OGA and the original artist to be made.

MedicineStorm is correct, however, only the copyright holder can bring suit for a license violation.  No one else has standing to do so.   This is not an assumption, it's the way the law works.   Think of it this way, sonething being GPL'd doesn't entitle anyone to demand source for something, it entitles the author to demand a distributor make source available.   So as he says, it would be strange indeed for an author to post a work here sans 'source' and then turn around and sue someone who uses it for not including 'source', what would be the point of that? 

Regarding your issue with using heroism, let me say well chosen!  It's a most excellent track indeed!  :)

Still, have you tried asking for the song in another format?

Out of curiosity, does debian specify what they want for 'source' for an ogg file?

If you're looking for a substitute, here's a recent submission with a similar feel to it:

http://opengameart.org/content/col-legno

"There is nothing in the submission guidelines that say that when you submit something, you implicitly give OGA the right to redistribute the work."
Note the word "implicit" here.  By uploading your work to a site that publicly hosts art you are giving the site permission to publicly host your art.  And in turn, if that direct permission is revoked we don't keep hosting work on the site, even if the relevant licenses would allow us to.  That's not done for legal reasons but nevertheless it's how things are run and it would likely provie a very formidable defense from anything frivolous.

As I've said, though, that only applies in cases where the sole author is uploading their own work.  Where third parties have uploaded it would just be under the terms of the license itself.  But that would likely clear the field even more.

It's only a little technical argument though--not much help for promoting the actual purpose of the site which is to provide useful, unencumbered freely-licensed assets.  But it could help stave off some complaints at the site itself.

@Redshrike: I'm sorry but I strongly disagree with that interpretation of how permission and distribution work on OGA.   OGA must distribute works under some explicit terms, and those terms are the licenses selected with a submission.

The alternative is that submiters are implicitly granting OGA the right to distribute the works however it likes or under some other unspoken terms, which makes no sense.

The bit about removing works upon request is just a courtesy and bear in mind even that is explicitly stated as conditional.  That is the site docs don't commit to removing works upon request, they merely state that OGA will try to honor such a request is possible.

Debian is the gold standard for strict licensing (thus the phrase "is it Debian free?"). If they have a hard time taking GPL art without sources, then OGA should ask for sources too. That is, if we decide to keep supporting GPL licenses (if not OGA, then who?).

I don't know, from gsliepen has described, when it comes to art it sounds more like an arbitrary standard than a gold one.

Is OGA the party doing the distribution, or is it the channel through which others are distributing the works?  Seems like petty semantics, but if it's the latter, I'd think OGA doesn't need to care about providing the source - the uploader is the party doing the distributing, and is therefore responsible for providing the source to those who request it (whether via a file upload here, a download on their own site, shipped physical media, whatever).  Is there any legal precedent regarding licensee responsibilities of user-content hosting sites like, say, NewGrounds or Wikimedia?  Does the Safe Harbor provision of the DMCA apply in a circumstance like this?

Honestly, this is why I despise viral licenses like the GPL - they're a bunch of vague, unenforceable nonsense that even the authors can't agree on the meaning of.  It reminds me of playing MtG with my friends back in high school: three hours spent arguing about the rules and the interpretation of card text for every half hour of actual playtime.  I release my own assets as CC0, because I want people to actually be able to use them without a f**king four-page discussion first.

**Edit: To be clear, any animosity above is directed at the authors of such licenses - it's good that OGA has a community that takes such things seriously and cares about both the artists and the users of the assets here.  I really just wish the organizations behind the GPL and CC-By-SA would clarify their murky language so we don't need to endlessly debate this stuff, as it's time the community could better spend elsewhere.

However this goes, we can start asking (politely) artists using GPL to include more adaptive formats for their assets at the very least.

I understand where Clint is coming from; we want to be the shining example of how to handle licensing. I just don't have the answers to questions like what formats do we accept? Anything lossy* is where I personally draw the line, but as gsliepen pointed out, that isn't flexible enough for many people (or entities... like Debian).

*EDIT: By "lossy" I mean single-file common formats like mp3, ogg, or jpeg. Lossless alternatives being wav, flac, or png. Obviously there are "super-duper-lossless" formats like monstrous zip files containing midi's plus the entire sample library used by that midi (midi's by themselves are insufficient for reproducing the same song! Each computer's audio samples have widely varying quality, so don't try to tell me midi sounds just as good from one computer to another sans the sample library!) or xcf/psd files with individual layers, or audio daws with all tracks separated and synth settings. But what do we accept? Only super-duper-lossless? Even if the artist produced their art in mspaint or windows sound recorder? We've had artists wanting to upload some of the extra "source-y" formats, but found they were unable to because OGA can only handle 200 MB uploads. Yes, the "source code" for a single song was more than 200 MB.

I have no doubt that any restriction on GPL asset formats we come up with will drastically discourage the use of GPL on OGA far more than it will encourage the inclusion of flexible "source" formats. I'm fine with that if you guys are.

> yes, source for one song can be over 200mb

Most definitely.  In my experience, 200mb would getting off light.

I'll also add that with the musicians I've had the privilege of actually watching work on a track live, the number of different tools, programs, plugins, sample banks, etc. etc. they use to produce a single song is stupefying.   It goes waaay beyond layers in a PSD.  And each musician does things a little bit different, to where wven if you had all the 'source' files for each step of the production, you'd probably still need a written guide to exactly reproduce the final track.

Thinking about it, source code has a similar 'everyone does it differently' quality to how it's assembled into the final binary.  But there you have make files or VS project files that provide a standard format for describing the process.  This just highlights again how the 'source code' analogy doesn't really work when applied to art.

I do get the idea of trying to be strict with license standards at OGA.  Just look at gsliepen and the heroic song submission, it's exactly the case you'd want to avoid, developer tries to use a work in accordance with the specified license but can't because there's a problem with the submission.

But honestly, lacking a clearly defined standard for what constitutes 'source', it doesn't seem worthwhile or fair to try and require submitter's provide it.   Especially since, as pointed out, it's the submitter who would ultimately have to file suit for someone redistributing the work without 'source'.

I think OGA should strive to be strict about licensing, but also think one of the wisest decisions bart has made with the site is not to make it dogmatic about what is 'free' or 'open'.   In this case, I think it's debian that's being dogmatic by setting up requirements that go beyond a simple reading of the license and are ultimately arbitrary as only they decide what they are and when you've met them.   

I'm reasonably sure RedShrike is correct that websites have an implicit license to redistribute works that were directly given to them by the legitimate copyright holder.  It's not always 100% clear what is included in that license and probably depends a lot on the context of what that website claims its own purpose is and what behaviors it conducts/operates (for instance, a site with ads or that sells products is more likely to be understood as commercial, and thus giving free stuff to one would plausibly be a commercial grant).  Note that the vast majority of businesses avoid this hazy area of implicit licensing because they want to be able to stop dead any lawsuit in summary judgement instead of going to far more expensive litigation and trial.  You've probably seen tons of hobbyist, personal, and non-commercial sites that would be dead in the water without implicit license, though -- a lot of them have no idea how copyright even works.

To a pretty extreme degree I think OGA being sued over anything here, GPL or otherwise, is vanishingly unlikely.  The site doesn't even generate enough revenue, directly or indirectly, to justify what a modern lawsuit costs.  Super low likelihood is not the same as zero probability, of course, so it's really up to the ownership to make a call on risk tolerance.

As for Debian, they're an enormous project at this point and they indirectly bring in or generate a lot of revenue (whether for themselves or those dependent on them).  Lawsuits are far more likely there, and hence why they set up such strict standards.  I still think some of the specific rejection calls Debian has made border on ridiculous.  When the copyright holder themself is telling you a usage is okay, it would certainly seem to be an all-clear, but they will gladly reject materials that don't match one of their preferred licenses.  The cost of this severe compliance is that some stuff will never be directly available or easily acquired by the user base, despite the fact that it's freely published on the web (often in multiple places) and already in use.

Perhaps the issue that capbros is hammering is really the biggest one.  Who will decide what preferred format is, if not the copyright holder (typically the same as the submitter)?  And if that is the (completely subjective) standard, what really would change from the status quo?

Getting back to the topic of what we should do about allowing GPL, at the very least it seems it would be a good idea to isolate them when selecting liscenses and put a notice above them the lisensing work under GPL requires you to upload the source files of the work or a written statement promising to provide the work if asked.

As a GPL software and games doesn't seem to need GPL work, removing it as an option may also work, or requiring non-GPL license (such as CC-BY-SA) to be selected in addition for when artists fail to upload the sources.

So if there's a common theme to this discussion and something I think everyone would agree on it's that GPL is not a good fit for artworks.

Given that, I guess it is reasonable to ask if OGA should continue to support it as a license for submissions.

There also seems to be a general sense that GPL is frequently selected by mistake.   It's either outright clicked by accident or added to a list of licenses by an artist just trying to make their work as useful to others as possible.

In that way, supporting GPL maybe doing more harm than good.  Or at the very least taking it away as an option wouldn't necessarily impact new submissions much.

One can also ask how useful it is to support a license that needs to have a bunch of flashing warnings around it because it's such a poor choice to use for art.

It'd be interesting to do an 'and' search and see how much GPL only artwork is on OGA now.

In terms of new submissions, just from what I've seen randomly clicking on new works over the past two years or so, I'd say GPL is a pretty rare choice, and GPL-only even rarer.   But that's just an impression, nothing scientific.   Still, my guess is that the CC licenses are far better known and understood now than they were back when OGA started up.  

I'm not against grandfathering in older submissions but I am starting to think maybe removing GPL as an option for new submissions is not such a bad idea.

• 136 GPL 3.0 only 
• 123 GPL 2.0 only
• 2 LGPL 3.0 only 
• 2 LGPL 2.1 only
• 88 which are some combination of the above 

351 Total which are exclusively GPL or LGPL. 

There are also an additional 1160 which include GPL or LGPL but are not exclusive, for a total of 1511 which use either GPL or LGPL in some way.  

The FSF's view is at https://www.gnu.org/licenses/gpl-faq.en.html#GPLOtherThanSoftware . They say it shouldn't be used if it's not clear what the source form is - but I can see cases where it is clear.

I'm not sure proprietary formats makes things fuzzy, the same could apply to any proprietary programming language. I'd say the preferred form is whatever the person used to edit, even if it's proprietary - this doesn't mean it has to be preferred by other people (someone might write in assembler and therefore release the assembly language code, the fact that I might prefer to work in something higher level doesn't change that).

It would be a shame to disallow existing gpl art out there even if we'd prefer a different licence to have been used.

The heroism/debian example shows that this can be a problem in practice, not merely in principle. Disallowing gpl altogether would have meant that music never got uploaded at all - which would have saved at least one developer time, but might have been a shame. Does the egoboo game contain the source? I see that egoboo is available on Debian repositories, so why don't Debian have a problem with that?

Whilst the GPL isn't as clear as CC0, the same is true of any licence out there, free or proprietary. People have their reasons for not releasing everything they do as public domain, and we have to work with that.

Thanks for checking. I wonder, what about things that are on Debian repositories - this seems to include Wesnoth and FreeCiv, which have gpl art/music don't they? What about SuperTuxKart? I think my feeling is, if Debian are ok with that, then there seems to be some inconsistency that Debian need to resolve. OGA might choose to take its own stance in advance if that, but we can't say "we're not allowing gpl for art because debian don't" if that isn't consistently true imo.

Or these games are also no longer on Debian repositories, or they don't include music and make an exception for sound/images, or they're grandfathered in, or something else? Depending on what the answer is, it could guide a solution here. (I mean, if the usually very strict Debian Free guidelines are ok with gpl for art in some cases, then it should be good for OGA, imo.)

The main reason for wanting gpl on oga in the first place seems to be for existing games like Wesnoth and FreeCiv, so it seems sensible to see how Debian have resolved that - or see if we can raise the issue with them.

Some old discussion at https://forums.wesnoth.org/viewtopic.php?f=9&t=2016 - seems they were happy to consider the files themselves as the source.

@p0ss: Thanks!  

Using the main search with any art type, all licenses and no keywords yields 14,439 results.

So by some quick calculations, about 10% of submissions check a GPL license, and about 2.5% check only a GPL license.

This is not to diminish the contribution any submission makes to this site, Heroic is a great example of a fantastic submission that we'd hate to lose.   But I think it is good to understand the scope of the issue.

Given these numbers, I think it's possible to say that the removing GPL only submissions would not be hugely devastating to the archive or the usefulness of OGA as a source for freely licensed game art.   And moreover removing GPL as an option for new submissions is unlikely to have a strong negative impact on the site.   That's even more true if you assume some portion of the existing GPL'd work is from older projects and new works are een more likely to use a CC license instead.   

I guess a follow up search to test that last assumption would be a count of GPL only submissions by year.

On the flip side, it also indicates that the scope of the problem is pretty small, meaning if we can live with a little grey, there's no burning need to change the status quo.

I'll add the numbers also suggest that the task of chasing after submitters for 'source' would be difficult and time consuming.   351 isn't a big number relative to 14,439 but it is a lot of submissions to review, contact the submitters and collect 'prefferred source' file for.   And the number is 5x worse if you consider any submission with GPL not just GPL only ones.

I'll be frank, if it's a choice, I'd much rather admin time was spent fixing search than hunting down 'preffered source' files.

@gslipen:  Funny you mention LGPL as I'm pretty sure that it was once a supported license on OGA but was removed to reduce clutter.

Finally, I just can't resist adding that the discussion of Debian and which games in their repo have or don't have 'preffered source' files for their music and art, highlights exactly how arbitrary their 'standard' is and previews the kind of fruitless tail chasing discussion we ca expect around every GPL submission if we choose to  go down the same path.

From Wesnoth's main README:

The game's source code and artwork, sound, and music assets are provided under the terms of the GNU General Public License version 2, or (at your option) any later version. Note that for artwork, sound, and music, we interpret "preferred form of the work for making modifications" as the modifiable form that the author chooses to ship us for the source tree. For convenience, a reference copy of the GNU GPL version 2 is provided in the COPYING file in this distribution.

Wesnoth has been accepted in Debian for years - this is not an obscure oversight, this is a fairly major project openly expressing an interpretation of the source clause which has been accepted readily by the Debian maintainers.  Does anyone have any Debian policy documentation to the contrary?  Not mailing list or forum discussions, but actual hard documentation of Debian's stance as an organization?

As a final parting thought, consider this consequence: under the OP's interpretation of the source clause, most CC0/PD works cannot be relicensed as GPL, since very few CC0 works include such a 'source form'.

"...we interpret "preferred form of the work for making modifications" as the modifiable form that the author chooses to ship us for the source tree..."

...Wesnoth has been accepted in Debian for years - this is not an obscure oversight, this is a fairly major project openly expressing an interpretation of the source clause which has been accepted readily by the Debian maintainers....

Wow. that... that is a good point, MoikMellah.

"Good point" is understating it ... that's a devastating counterargument to OP's contention that there is a worthy issue here at all.  If even Debian, noted fanatics for copyright compliance, don't care about this then I cannot see any reason for OGA to bother.

What I am getting from this is that we shouldn't have admins decide what constitutes source material. It would take a lot of time and not even Debian can agree on it.

Let Debian worry about what Debian will accept and find a way to encrouage people to upload sources with GPL.

Honestly, a little text above the GPL liscense reminding people to upload thier sources if they use this liscense and some text that would appear by the submit button that says 'By clicking submit you certify that you have uploaded the sources for these files" that appears if you select it would be enough to keep using GPL.

I don't think that was an excuse to ignore the source requirement, it was an example of the artist defining what constitutes source. In that case, the artists contributing to wesnoth aren't ignoring the source requirement, they're saying the assets they submitted are the source.

With code, the definition of source is fairly obvious. With art it isn't nearly as concrete, so they (wesnoth) defer to the preferences of the artist. "preferences" being directly related to "preferred form of modification". This interpretation being accepted by Debian, including newer submissions, not just grandfathered-in stuff from way back in the day, is relevant.

A friend of mine created a small game in machine code... because he's crazy. No, not assembly; Machine code. (He's since made it available in assembly so others can learn how to code like it on their own machines. see http://xlogicx.net/?p=515 and https://github.com/XlogicX, especially https://github.com/XlogicX/tronsolitare etc.) Regardless, there is no true source code other than the machine code itself. What happens when he releases it under GPL? He is the copyright owner, his preferred form of modification is direct bit manipulation of machine code. Will Debian like it? I don't know, but who can complain about him. He's the only one who has the right to complain about his own source. This is an obvious fringe case, but my point is that "preferred form of modification", especially pertaining to art, remains nebulous.