[Plishar]

I make games all the time for myself, sometimes using copyright protected images. But I can't share the source code or publish the game in Google Play if I do that.

If I want to share or publish, I have to use free stuff or make it myself. If I want to use copyright material and publish it, I need permission and a contract with the owner of the IP, a license or agreement of some sort to use their stuff.

All this applies to everyone, not just the US, if you want to do business. If it's just for fun that's fine but you can't distribute it in anyway, including github.