This isn't DRM right? This is metadata attached to the image that makes it clear it was synthetically generated. The public has a huge incentive to know when images are AI generated and the harm to legitimate users seems pretty small: aka someone might complain online that you use AI

Not yet, but it is easy to imagine many ways it would be used for DRM.

billions? of "fake" images not generated by ai but just photoshopped and ... not really harmful.

There is no case that any of its particularly harmful outside of things like CSAM which is illegal.