caeles, I missed the part about GPL requiring source form. That is an important part of the GPL too. Thank you for pointing that out.

My issue with GPL on artwork is GPL is designed for something that can be compiled/interpreted and executed. Artwork (aside from complicated cases like 3D models and vector art with embedded scripts) is entirely static or markup content with no parts that can be compiled/interpreted. The significant part of that is it must be executable; artwork is not executable on it's own, it must be rendered by something external. From my perspective this means all artwork are static data. Most of the GPL text doesn't have meaning on artwork except the three main clauses we've covered already.

GPL on artwork causes the following:

1. Attribution
2. Prevent DRM
3. Require source version

All of those things are desirable outcomes for artwork, that's why I included GPL as an option on all my assets listed on OGA. While GPL is a software license it does have some traits that make it useful on graphics. The most notable trait of GPL, that of causing an entire project and all it's software components to be forced under a GPL license, doesn't work with artwork or other static resources. That's the main thing I would point out.

EDIT

For a reference to the GPL and why this is true please read the last large paragraph under heading 1. Source Code, found here (The “Corresponding Source”):

https://www.gnu.org/copyleft/gpl.html

This paragraph explains how externally linked resources (interface definition files/shared libraries/dynamically linked subprograms, i.e. artwork) are not absorbed by the GPL when included in a project coverd by GPL.

[...it does not include the work's System Libraries, or general-purpose tools or generally available free programs which are used unmodified in performing those activities but which are not part of the work.]

Unless artwork is embedded in the program, such as directly including the binary that describes the artwork into a class definition, then it cannot be considered an essential part of it. I can swap graphics in a generic game engine all day long, none of them are essential for making the engine work.

It might seem like I'm splitting hairs by saying graphics can't force the GPL onto software but let me demonstrate with simple thought experiments.

Example #1:

Let's assume I have a GPL image on a server that someone can view with their Internet brower. The browser must download that image and render it from a local cache using system libraries. Since that browser must open and render the image does it now become an integral part of the browser and cause the browser to rely on it to function? No, the image cannot force the browser to rely on that image to function, thus it cannot force that browser to take on the GPL.

Example #2:

Let's assume I have a GPL image on my local drive that I want to view with a non-GPL image viewer. By opening the image with this viewer software does it now rely on the image to function? No, the viewer is a separate program that is dynamically linking to the image file to read static content. The image cannot force the viewer to fall under the GPL.

Example #3:

Let's assume I have a generic program that reads and interprets image data from external files (let's call it a game) and displays them on screen according to pre-defined program logic. Now let's say I open that program and it reads data from a GPL image. Does that program now rely on that image to function? No, I can replace the image file with a new file at any time, it is not an integral part of the program. That GPL image cannot force software to fall under the GPL.

Is this clear enough or should I continue to beat the dead horse?

EDIT

Just in case we're not completely clear let's have more examples.

Example #4:

I have a GPL image on my local disk. I embed this image in an MS Word document. Does the document become GPL as a result of the image? Does MS Word now become GPL because of the image in the document? MS Word does not rely on the document to function, so it cannot be GPL. The document is not GPL since it can contain other elements besides the image. Only the image is GPL.

Example #5:

I have a GPL image stored in an archive file. Does the program that reads the archive become GPL because of the image? No, the program that reads the archive does not rely on the archive to function. The archive file doesn't become GPL either because it can contain more than the image. Only the image file is GPL.

Example #6:

I have a website with a GPL icon. Someone bookmarks my website and the icon is stored by the browser and gets displayed in their favorites. Now their browser displays this image every time the favorites list is displayed. Does the browser now rely on this icon to function and fall under GPL? Hell no. The browser is driven by program logic that interprets display data given to it by the user, it does not rely on the icon stored separately from the browser to function. The GPL icon cannot force the browser to take on the GPL.

These examples apply equally well to the argument that CC-BY-SA assets somehow force an entire project to fall under CC-BY-SA. Program logic and display logic have been legally separated for decades for exactly this reason. It hasn't changed since GNU and CC started making licenses.

This is only an issue now because people want to pretend games don't fall under the same traditional model of software development that operating systems and most end-user programs use.

How could Microsoft make AutoCollage when it behaves similarly to a game? It relies on more than 2 external image files to produce a unique display that contains both images at the same time, regardless of the license on either file. The program logic is independent of the image files.

How can the Quake game engine be released under the GPL but the content used in their game be under a different license? Simple, GPL doesn't glom onto graphics the same way it gloms onto software components! If it did, the Internet would be the biggest breading ground of lawsuits ever conceivable by mankind since Internet browsers display images.

Two paths of ethical philosophy to consider:

1. Conservative legalistic self-righteousness path. The artist's intention for the licenses they chose is what matters, but you have no way of knowing what their interpretation of the licenses are. So, when in question about the license, always lean in favor of the artist's most restrictive possibly intention. That way you are "doing what is right" no matter what and sacrificing what benefits you (and possibly them) to that end.

2. Screw it. Use CC-BY-SA and GPL licensed artwork in your closed-source commercial game. If your game makes no money, the artist has nothing to sue out of you and won't bother to take legal action. If your game makes heaps of money, you're rich, so it's no deep skin to rightfully settle with them at that point and give them a chunk of change. They deserve it. This is the "let the legal aftermath figure it out" path. That's exactly what legal aftermath is FOR.

So, open question to everyone. Which ethical philosophy do you ascribe to?

I try to make sure everyone is happy so I end up asking everyone for permission even if they have a clear license. I guess I fall into the first category you outlined.

I believe that is the most comfortable path for me as well. My 2 points illustrate opposite extremes to invite discussion. Anyone else have any thoughts?

@William.Thompsonj: I'm not taking sides as such on whether GPL can apply to art, but I'm not convinced by those examples. For examples 1-3, and 5-6, couldn't you have the same examples for code? E.g., a browser that downloads a GPL plugin to display the content, or if I view a generic program thatt reads and inspects a GPL program (e.g., debugging tools).

The fact that a GPL item A can be read by program B doesn't force B to become GPLed - and that is what is intended, whether A is a program or art. This isn't a problem, because the GPL was never meant to cover those examples. The issue is when B is distributed with A (a "covered work").

As you note, the examples apply to CC BY-SA. I don't think people saying the GPL applies to art want it to apply in these examples - they're talking about when an art is redistributed with a game.

For example 4, applying the GPL to art might mean that the entire document must be distributed under the GPL. But isn't this also the case for CC BY-SA? MS Word however certainly doesn't become under the terms of the GPL, because you're not distributing it - just as it doesn't become CC BY-SA, just because you loaded a CC BY-SA image.

mdwh, fair assessment. Still, how can the Quake game engine be released under GPL and the content remain private? That begs me to ask how GPL can force art or other interface content to be covered by the same license, even if distributed together, when a major game company like Id Software has done exactly that. Id Software distributes their game engine as GPL and their content as private license and distributes them together. Obviously this is a real-life example that begs me to ask how GPL affects interface content in any software, not just games.

By the way, if you want a more modern example (one that involves a derivative of a GPL engine) here's another dicotemy to consider:

All the Half-Life game series uses a modified version of the Quake engine (GPL), yet all Half-Life content is held under a closed-source license.

Explain to me how GPL software can change content licensing? or how content can force software to change it's license?

Okay then how about something a little closer to home. How can FLARE be under the GPL while the content used to make games for it be under a different license without violating either's license?