Europol has supported authorities from 19 countries in a large-scale hit against child sexual exploitation that has led to 25 arrests worldwide. The suspects were part of a criminal group whose members were engaged in the distribution of images of minors fully generated by artificial intelligence (AI).
Some form of digital signatures for allowed services?
Sure, it will limit the choice of where to legally generate content, but it should work.
I highly doubt any commercially available service is going to get in on officially generating photorealistic CSAM.
Open-source models exist and can be forked