[oclero]

Hahaha these licenses are a real nightmare 
By the way, the GPL logos are  CC-BY 3.0 ! We should follow their example for Solarus logo, am I right?

[Zefk]

Yes, licenses are a pain. Everything should just be free!

[Diarandor]

More interesting links here.

A compatibility analysis of CC-BY-SA 4.0 and GPL v3:
https://wiki.creativecommons.org/wiki/ShareAlike_compatibility_analysis:_GPL

More about the CC-BY-SA 4.0 compatibility with GPL v3:
https://wiki.creativecommons.org/wiki/ShareAlike_compatibility:_GPLv3
https://creativecommons.org/compatiblelicenses/

In the links above they explain the one-way compatibility mechanism of CC-BY-SA 4.0 with GPLv3, which (as they state) is not for general use.

My conclusion/interpretation of all of that (which could be wrong, so please correct me in that case) is that:
1) CC-BY-SA 4.0 art can be used when creating GPL v3 software (i.e., when a compiled program is created), and it becomes GPL v3 in that process. I think it is not possible to directly change the license from CC-BY-SA 4.0 into GPL v3 unless a compiled software is being created, and the change of license into GPL v3 only is applied to the image as part of the software and not to the original art files (or modifications).
2) There is no way back from GPL v3 into CC-BY-SA 4.0 because this is a one-way process.

[Zefk]

2) There is no way back from GPL v3 into CC-BY-SA 4.0 because this is a one-way process.

That is true for people other than the creator. The creator can do whatever, but the logos are under CC-BY 3.0 as well, so the graphics can currently be used as GPLv3 or CC-BY 3.0

A lot of opensource games have the "content or graphics" as GPL. Maybe they are wrong or they "interpret" it differently.
https://en.wikipedia.org/wiki/List_of_open-source_video_games

[Diarandor]

Yes, of course, the creator (or copyright holder) can do whatever he wants with licenses. I was talking from the point of view of other people which are not the creators.

It is hard to know if other people do it correctly or not. Anyway, in previous licenses (GPL v1 and v2, and CC-BY-SA before version 4.0) things were a bit different, so maybe the best way to do it was different, who knows... But that does not matter to us, so forget about that.

[ninawilliam89]

  sorry. version for your phone?

[Zefk]

sorry. version for your phone?

Here is a pdf version: Here

I hope that helps on your phone or Android. You will have to login to download it.

[Zefk]

Update:

I just learned that CC-BY-SA 3.0 is compatible with CC-BY-SA 4.0.

The following adjustments were made:

That means a CC-BY 3.0 pieces can be combined with CC-BY-SA 3.0 and released as CC-BY-SA 3.0 or later.

Source: https://creativecommons.org/share-your-work/licensing-considerations/compatible-licenses/
"Adaptations of BY-SA 3.0 materials may only be licensed under BY-SA 3.0, or a later (4.0+) version of the BY-SA license."