This is similar to the discussion here: https://opengameart.org/forumtopic/licensing-question

There is also some information on this in the FAQ here, and here.

animations, comics, and sprites would all apply the same way under GPL. The simplest way (or the "playing-it-safe" way) is to use GPL artwork in a GPL project with GPL code. However, there is a lot of discussion on if that is truly necessary. You'll have to do your own research, but here's my overly simplified summary of the issue:

• GPL is not the recommended license for art, but there are legacy reasons for maintaining it as an art license.
• GPL'd art doesn't neccessarily mean the code must be GPL as well. Art and code in a single project may be licensed separately as independent "collections". However, each project is subject to unique circumstances. Consult your lawyer if swelling persists longer than 4 hours.
• If you're submitting GPL artwork, it is preferable (and polite) that a highly-editable format of the art be included along with a more finialized form. E.g. include a photoshop PSD file (or gimp XCF file) along with a PNG or JPG image of artwork, so other users may modify the image easily. Whether or not this is required in order to be compliant with the GPL is unlikely/debatable, but still a good idea.

Other similar discussions if you feel like reading a lot:

• https://opengameart.org/forumtopic/question-about-gpl-assets
• https://opengameart.org/forumtopic/licenses-0
• https://opengameart.org/forumtopic/question-about-gpl
• https://opengameart.org/forumtopic/attribution-and-licenses-0
• https://opengameart.org/forumtopic/question-about-gpl-license
• https://opengameart.org/forumtopic/license-question
• https://opengameart.org/forumtopic/gpl
• https://opengameart.org/forumtopic/license-clarity
• https://opengameart.org/content/not-completely-sure-about-licensing

If that doesn't answer your questions, say so and the community will do our best to help, but as you might have guessed, it's unlikely to be a very simple answer. :)