-SA and GPL are okay, as long as you make any deriviative work available under them as well.

I.e. if you take some -SA/GPL concept art and create a 3d character, you'll have to make it free as well. That doesn't concern other character on your project. I.e. there is nothing wrong with Nintendo using Sara (OGA maskot) in some Mario Galaxy, although Nintendo will have to release all changes to Sara under -SA/GPL

Although there are some nuances with CC- and GPL licenses used with Apple's store, which has a license, that gives Apple some additional rights over them. TLDR: Apple is evil and doesn't respect developers and users.

LGPL is the same as GPL for the purpose of shared libraries and artworks, unless you convert them to C/C++ code and link into your program at compile-time. Otherwise loading a GPL'ed png file is equivalent to calling dlopen, which is okay and doesn't invoke GPL linking clause. Same way you can dlopen GIMP's executable from your closed source program and provide all gimp's funcionality.

OGA-BY gives Apple additional rights over your art, so it can be used with Apple's Store.

>So, for LGPL is ok (for "closed-source projects") if I load a image and maintain the format (like HTML5 and Flash do) but is wrong if I have to convert it to a compiled format (like XNA with the .xnb format)? I'm thinking right?

Yeah. For GPL and -SA you'll have to provide the original source material.

>So if I want to submit a game for greenlit/appstore/google play I just have to take caution about how the engine reads the LGPL files (sounds, sprites, etc)?

You cant legally submit GPL/LGPL/CC stuff to Apple's Store:

http://www.fsf.org/news/2010-05-app-store-compliance

LGPL isn't allowed either. So AppStore hosting Battle for Wesnoth is actually infringing GPL.

Only OGA and Public Domain allows that.

>About Apple... What is the additional rights added to CC-BY? I read about some technical measures that CC-BY have and OGA-BY don't, what is this technical measures?

The primary problem is that Apple imposes numerous legal restrictions on use and distribution [...] through the iTunes Store Terms of Service, which is forbidden by section 6 of GPLv2. S

CC-BY-SA, GPL and LGPL

Here is more on the problem with Apple Store:
http://lwn.net/Articles/391423/

>Apple's App Store terms of service do impose several restrictions, such as limiting usage of the program to five devices approved by Apple.

CC and GPL licenses don't allow additional restrictions, like tihs relicensing.

Apple introduced such restrictions to disallow running AppStore programs on iOS-compatible devices.

 I.e. Apple thinks it owns everything on AppStore.

They are okay for closed-source projects. Just not okay for AppStore, which requires relicensing them to Apple.

"FSF has clarified that use of art does not trigger the GPL's linking requirement"

moreover, the linking requirement applies only to compiletime linking. I.e. loading a library with dlopen (or fopen) doesn't require you to opensource your code.

Yes, I agree with what Nikita_Sadkov said. The GPL 2.0 and CC-BY-SA 3.0 do mean that you have to open your "source", but if it's a PNG image we are talking about, then the "source" is very likely the PNG file itself. And your game's executable isn't a derivative work of the image, so you don't need to open your game's executable's source.

Please note that the GPL (version 2 and 3) define the "source code" as follows:

• "The source code for a work means the preferred form of the work for making modifications to it." (from the GPL v2 section 3)
• "The “source code” for a work means the preferred form of the work for making modifications to it." (from the GPL v3 section 1  Source Code.)

So although a png is an acceptable form of "source code" distribution (for images) you have to be careful not to destroy data useful for editing (like layers for example). Since these are generally not wanted when using the assets in game a separate "source code" distribution of assets may be useful.

Of course if your file does not have this sort of information (and you do not add it) you are probably fine.

So let me toss in there that if you modify the source png's in any way (like say, changing the spacing or layout for a sprite sheet, or combining two or more images into one texture, or saving as a different format) then you are out of 'loading a dll' territory and potentially into 'derivative work' territory.

Also, everything Nikita_Sadkov said about Apple, assume that applies to every other digital distribution network or will apply once their lawyers get around to it.

Additionally, the 'technical measures' restriction is generally interpretted to mean 'NO DRM.'  There seems to be some debate about what platforms use DRM and to what extent.  IOS, PSN and XBL almost certainly count as 'DRM'ed' platforms.  I've heard arguments both ways on Steam and Android.

Generally, I'd say if you want to play it safe, you're list should look like:

safe for commercial/closed source projects:
cc0

oga-by 3.0

unsafe for commercial/closed source projects:

anything else!

For cc-by stuff, commercial distribution might be ok if you are using a DRM-free PC installer and distributing only on sites that directly redistribute your installer (things like itch.io, etc.) and not on sites that repackage your program for their own download clients (GMG, etc.).

Again, this is play it safe advice.  If there's something CC-BY or whatnot that you just have to use in your project, I'd advise you ask the artist directly.  The original author can always grant you a waiver and folks can be pretty accomodating as long as you are polite and nice about how you ask.

From the FAQ: "some of the licenses require you to distribute the source code of your entire project for free, and allow others to distribute the source for free as well."

I think that may be just wrong in the FAQ. IIRC originally the FAQ claimed that CC BY-SA meant you had to release the source (which isn't true). I see it no longer says that under the CC BY-SA section, so I think it's been updated, but possibly that bit quoted above wasn't updated.

Regarding sites that apply additional legal or technical restrictions, this would apply for all projects (including Open Source), not just closed source or commercial ones. I'm not aware of any problems for Google Play?

Either way, this relies on the game's executable being a derivative work of the art, which is very doubtful.

In any case, using a digital distributor hardly poses an issue for open-source software, as long as you make the source available, and you don't use any closed-source libraries.

@Andrettin:  

>  using a digital distributor hardly poses an issue for open-source software,

> as long as you make the source available, and you don't use any closed-source libraries.

I don't know for software, but for CC-BY 3.0 artwork, it seems subject to debate if simply making the original material available somewhere is enough to get around the anti-DRM clause.  The idea being that if you are distributing it on any platform that imposes 'additional technical measures' then you are imposing 'additional technical measures' regardless of what you do elsewhere.  

My understanding is that if it's made available elsewhere, then there are no "effective technological measures on the Work that restrict the ability of a recipient of the Work from You to exercise the rights granted to that recipient under the terms of the License". It's not effective if the artwork can easily be gotten elsewhere; and that's not to enter into the question of whether digital distribution software is "DRM". I imagine an effective technological measure of this sort would be like putting the artwork in a proprietary file format which only you have the know-how to open and edit.

@Andrettin:  Yeah, that's one way to argue it, but like I say, I've heard it argued the other way also.  At the very least, the idea came up during the discussion that lead up to the creation of the OGA-BY license and there was enough uncertainty about 'separate but open' distribution as a satisfactory solution that the OGA-BY license was still created.  There were other reasons for creating OGA-BY too, of course, I just mean this idea was discussed and not everyone agreed that it was acceptable way around the anti-DRM clause of the CC-BY license.

@mdwh: I have heard Andriod apps argued both ways with regard to DRM.  I would say unless you've had a lawyer go over line of the distribution agreement, I'd assume that the system either has DRM or has the potential to have DRM in the future, or probably imposes some other unacceptable legal restrictions on the work.

So I guess that's why I called it a 'play it safe' list.   Basically, rightly or wrongly, I've heard it argued all ways on the other licenses, so my advice would be to steer clear of them for closed source/commercial projects.  CC0/Public Domain is pretty widely recognized as ok to do with as you please (although I must admit, I've seen even that debated on these forums ;) and OGA-BY was created with the explicit intent of supporting closed source, commercial projects and distribution on DRM'd platforms.  So those two seem safe bets to me.