The artist is violating copyright by selling you that picture. You can’t just start creating and distributing pictures of a copyrighted property. You need a license from the copyright holder.

You also can’t sell a machine that outputs such material. And that’s how the story with GenAI becomes problematic. If GenAI can create the next Indiana Jones or Star Wars sequel for you (possibly a better one than Disney makes, it has become a low bar of sorts), I think the issue becomes obvious.