From what I'm seeing, probably none of them.  "All rights reserved" is not a very FOSS-friendly kind of phrase, and none of the text gives a clear idea of how you want the art to be treated.  If you want to relicense/dual-license the art assets to be OGA-compatible I'd suggest that you read through the descriptions of the licenses used here and see if one of them fits what you want.

Look closely at the license text. It's actually the 3-clause Modified BSD License, which is GPL-compatible and approved by the OSI. It does seem like an odd choice considering that Freedoom isn't really software, but it is generally considered a free license. The site already has the less permissive GPL available, and I'm actually kind of surprised BSD licenses aren't available too.

@XCVG: Fair enough, I spoke too soon.  I guess it's going back to the issue of using software licenses for art.  That said, it would probably still be best for the artists to select a more art-focused license choice.

FreeDoom has been around a long time, possibly before the CC licenses came into existence (or at least before they become well known and commonly used).  I agree that using a CC license would be better, but there are a large number of contributors and it just wouldn't be feasible to contact them all in order to relicense everything.

BSD-style licensed code is often used in GPL-licensed software, with the whole program being under the GPL license, and that's all perfectly legal and common.  But when it comes to art, it does seem a bit strange (to me) to relicense under the GPL, e.g. to upload to this site.

I think BSD is more equivalent to CC-BY, or even CC-BY-SA, but BSD allows mixing of licenses whereas CC-BY-SA is iffy on that. CC0 (Public Domain) would be nice, but CC-BY 3.0 would be acceptable too in my opinion. CC-BY-SA can cause issues with license compatibility and some people avoid it for that reason.

My suggestion is to get permission and relicense as much as you can, even if it's not the whole project, and post it here. Freedoom is big, and even a relatively small portion could be quite useful to a lot of people.

Were you able to get any of the assets relicensed?

Perhaps not me personally, but someone will. I've seen some of your work on the ZDoom forums and if you released it under a libre license it could be useful to a lot of people.

From what I have been reading here:

Those are very good options, additional to this - consider the OGA BY 3.0 licence when uploading to this site - as this ensures no conflict with iphone released games/apps etc.

Only CC-BY.

CC0 has no restrictions whatsoever.

If you are interested in more details about how OGA-BY 3.0 was created/was needed, read about it here:

http://opengameart.org/forumtopic/new-license-proposal-in-response-to-drm-waiver-discussion

Yeah. We have got similar problem wtih Blasphemer assets http://opengameart.org/comment/36753#comment-36753

asking people to re-license because of some single site would be a waste of time, when assets are free anyway.

I think it would make sence for somebody to fork OGA, at least for BSD or CC-BY-NC licensed art, which should be okay, since OGA doesn't hold copyright for any of its content.

Regarding CC-BY-NC art, what would constitute commercial use? For example, can somebody create a mod for GTA5 using CC-BY-NC licensed art? Because GTA5 is a commercial product, so any content made specifically for it will increase its commercial utility. Would hosting NC content on a site, that shows ads, will be commercial use? I.e. EA can secretly hire some 3rd person to create an addon for their game and this person will release it for free (no NC violation, yet profit).

You need to get written permission from authors. Usually an email from them stating such in clear terms is fine, for example get them to reply "I hereby give permission for my work XYZ to be licensed under the foobar license".

What if there are 9000 authors and some are unreachable or against changing license?

Why would they change license because of some site/organization not accepting BSD-licensed contributions?

If there are 9000 authors, then you can only submit art for those authors who agree to change or release using oga supported licences.

i.e - if only 5 people respond - you can only submit the work from 5 people.

I think this issue is a little off track - in that the resources in theory should be hosted here - but simply cannot due to the current rules.

Perhaps we need to either add the BSD licence - or add new features that allow submission of 'free' but not supported resources - perhaps new functionality that shows warnings - and may host previews here but not the actual files (perhaps only links?).

Currently the site rules are pretty clear - that these files cannot be hosted here.

The discussion now needs to be about what can be done so that these resources can also be included in some way?

Redshrike says BSD allows submiting these assets under CC-BY

http://opengameart.org/comment/36794#comment-36794

I.e. there is no need for relicensing.

Just to toss it in there, CC-BY has the 'technical measures' restriction, which I don't think is part of BSD license.

So wouldn't a better choice for BSD stuff be OGA-BY?

Although, IMHO, if BSD licensed art is going up on the site, it should be listed as BSD license.