And if you DO use photo reference, unless it's a stock photo, then to be safe you should have the photographer's permission, which usually involved paying them something.

But people certainly get around that. It depends on whether or not the original artist/photographer catches it, and has the resources themselves to pursue action. This is of course where corporations have huge advantages over individual artists.

The whole copyright/trademark thing does get pretty complex, doesn't it? A few years back my partner and I tried to study it and even went to a legal group for artists in NYC, so we could figure out what to put down on the contracts with her clients, and there were only more questions than answers.

I've got friends who basically make their living selling fan art.

I'd better not mention this to my sweetie, who hopes to make an income in retirement from her paintings. (Which are good, but an actual income? Not so sure about that.) Unfortunately she's not a fan of anything in particular, so that would be a no-go.