How do you enforce copyrights for projects, in different countries, against open-source projects or modifications? You effectively don’t against small players, but you put enough laws to at least deter any large enough party from doing it too overtly. And for countries that are actually hardasses for IP laws like the US, you can make it scary enough for anyone to attempt commercial use of unmarked AI content (lest they get caught), just like you have made it with making commercial use of copied stuff from content not licensed to you.