Calimero000 said:

But is it already not OK when people do it and you don't know about it, or does you getting to know it make it not OK? Because in the former case, in theory, everyone in the world except you could know about it and you would be OK with that.

Yep. I actually wrote it thinking that you might make that kind of objection, but I totally agree that everyone in the world except me could know and I'd be OK with that (assuming that I wasn't trying to profit from the image, or otherwise need to control it). It's all about how easy it is to derail the artistic process. If your train doesn't bump into my train, no problem.

Of course, if you do it once, you might do it again. So it also has to KEEP not bumping into me, in this scenario. Which I think is fairly unlikely.