@riana I think the realism argument is typically exaggerated (even the people who argue it tend to contradict themselves). Even in that case, I'd find a "War on Drugs" type tending to violate civil rights prohibition approach to be suspicious. It's not clear it wouldn't end up doing more harm than any possible good.

I think the most effective thing might be to deal with conduct points (i.e. sextortion, harassment, maybe invasion of privacy), as these seem to be what people are worried about, rather than making broad content based prohibitions (which tend to violate human rights, and likely involves "non-existent people"). It's not really effective, proportionate, or sustainable, and it would drive the surveillance / carceral state, and the harms inherent to that.

Also, the contexts in which someone has cited it being present (i.e. criminal sites which already clearly violate 2251) would suggest they could already be prosecuted for that other criminal conduct.

It is also not clear it is a significant issue. It seems exaggerated, and it seems every month, someone is arguing the end might be right here, although with hardly much new to argue with. Examples are usually like "this site or that site", and often, there is language which quickly makes it sound a lot like "non-existent people".

That said, I don't necessarily disagree with your suggestion for authenticating the image provenance. And perhaps, if something is less "black market", then there might be more incentive for a service provider (which deals in such things, not a mainstream one) to assist in that, than if they're liable either way.

Also, in that other country where it seems to be protected speech, the arguments look a lot the same. It is argued that a prohibition would violate the Japanese Constitution which protects free expression. As far as I know, the Supreme Court there has ruled that it could be restricted in the case of something depicting actual children.