While browsing through OpenGameArt.org for ideas and possible resources for Ludfesto and beyond, I saw a thread called Practicality of CC-BY-SA (active at the time of this writing). Having recently decided that I would want to release game resources under the CC-BY-SA license, I saw this as very relevant. I read through a number of the comments on the post, and decided to explore some of the main questions that kept reappearing with respect to copylefted assets in video games.
Please note that these are my own opinions and speculation. I am not a lawyer, and I have no affiliation with Creative Commons or any other authoritative organization.
Question 1: Can I include CC-BY-SA assets in a proprietary video game?
I think that the answer to this is “no,” but that is because of my belief that video games, unlike most other types of software, are art. If video games are art, then they are derivatives of their assets, so if their assets are copylefted, then the game itself must be copylefted.
If a game is not considered art, it might not be considered a derivative work. Just as photo-editing software is not considered derivative of the photos it can load, a game that loads potentially arbitrary assets could be argued not to be derivative of those assets, so license compatibility is irrelevant. This view is common in the OpenGameArt thread, and makes sense if video games are indistinguishable from other types of software.
The problem with the existence of multiple interpretations is that, unless there has been some legal precedent, an individual that wants to use CC-BY-SA assets in a proprietary game cannot be sure that this is legal. For this reason, many people in the thread said that the discussion dissuaded them from using CC-BY-SA for their art. For a conversation in a community built around the idea of sharing work with others, there was a surprising number of posters who either disliked the idea of FOSS or felt ambivalent about it.
Question 2: If I use CC-BY-SA for my art, does that mean that people can’t use my art to make commercial games?
No. This question conflates “proprietary” with “commercial,” and “free-libre” with “free-gratis.”
The GNU website has a good article about charging money for Free Software.
A copyleft license just means that when you distribute your work to someone, however you decide to do so, they have the right to redistribute it under a compatible copyleft license. It doesn’t mean that you have to distribute it for free (i.e. without charging money).
Question 3: If a game uses CC-BY-SA assets, do screenshots, screencasts, or other captures need to be licensed under CC-BY-SA?
This depends on the purpose of the new media. Possibly, you’re using this new media in a way that falls under fair use. Criticism, parody, and education are all uses that are protected to some degree under fair use. If your use falls into one of these categories, it’s possible that the license doesn’t matter, and you don’t need to get permission from the original creator of the media/artwork/video game. Make sure you read up on fair use before you assume it applies to your work.
If your use doesn’t fall under fair use, then I think you can be safe in assuming that it counts as a derivative work. Are you publishing a screenshot to show something that you’ve been able to do in the game (an achievement, funny bug, or in-game creation)? Are you streaming or videoing your gameplay to show an audience your play-style or to give the audience an experience that they wouldn’t get from a trailer or review? If so, then you’re very clearly making a derivative work. If all the content visible or audible in your derivative work is CC-BY-SA, then by the license terms, your derivative work must be licensed CC-BY-SA (or something compatible, if that exists).
If the content is of mixed licenses (as could be done with an engine that loads user-defined resources locally), then you’ve got to license your derivative work appropriately. If you’re working with CC0/Public Domain media and CC-BY-SA, then you’ve got to use the CC-BY-SA license.
The unfortunate part is when you’ve got conflicting licenses: say some CC-BY-SA media and some proprietary media. The CC-BY-SA media requires you to license derivatives as CC-BY-SA, but perhaps the proprietary media disallows copyleft derivatives. I think the sad solution to this is simply that your derived work cannot be published, but maybe there is a legal and ethical work-around.
Question 4: Wouldn’t CC-BY be better?
This is a question about Copyfree vs. Copyleft, and the answer is probably something like, “Whatever works best for you, and fits best with your idea about how to promote Free Culture.”
If you want to allow people to use your work in absolutely any way they see fit, as long as they attribute your contributions to you (or maybe even without attribution), then CC-BY, CC0, and Copyfree licenses in general are what you want.
If you want to allow people to use your work in ways that force the propagation of Free Culture, then CC-BY-SA and Copyleft licenses in general are what you want.
I may come back to this post and edit/update it if my views change, or I see that I’ve made a mistake (and I’ll let you know when/if I do with an [Edit] notice). I know that I will definitely make a post about Copyleft vs. Copyfree philosophies in the future, because I don’t know where I stand, and I think it’s an important topic to explore. I’m also aware that there are ways in which the CC-BY-SA and the GPL are incompatible, so I’d like to explore that as well.
Please comment and let me know what your opinions are on the issues discussed here, and definitely let me know if I’ve gotten something wrong.
[Edit 2014-12-16] Upon re-reading the post, I found that my original answer to Question 1 was not adequately descriptive of the subtleties of the question, and that I had made some stylistic and grammar mistakes. I also added some more hyperlinks to resources for terms and ideas that readers may be unfamiliar with.