Copyright protects against distribution of protected media, if you don't release anything with that media then it's not a thing.
Really, the methods by which the copyrighted media is created means nothing - we could just say that any compressed image format does the same thing, it generates the media from encrypted data - no different to generating the media from code.
It boils down to the individual companies involved... some companies will nab media from wherever they can get it and not care too much if people nab it from them in return - but some companies will get lawyers involved even if your game has a passing resemblance to their IP. Some companies IP is worth millions in revenue and has to be protected. I mean, what would happen if Nintendo let people make Mario games for any platform - instantly their share price drops through the floor (further I mean).
Personally, I think that if an artist takes their own digital images and makes textures or whatever from them, or makes them from scratch - they have the right to protect that work.
But if an artist googles for a base texture, the shouldn't have the right of protection, because they can't guarantee that the originator of the base texture is protected. If it's out there then it has to be public domain, even if it has a watermark you should still be allowed to legally use any media that is made directly available online. That's not the case, and we are in the same situation that we've always been - the company with the most lawyers ultimately calls the shots.
I've had media nabbed before without notice, permission etc for a commercial game, but if I went and uploaded my textures somewhere, I might get in trouble for that. That's one messed up situation. I doubt very much that the company involved would do anything, or even care very much - but we can't assume anything. It's a can of worms and copyright lawyers make good money from it and big companies can have their own way everytime, us little guys don't stand a chance, we have to steer clear of questionable content and forgo justification sometimes.
I am the one who knocks...