What about giving a censored version of the appropriate image? Like put a big black rectangle covering whatever awful thing is the subject, and just (e.g.) show some feet and hands and a background.

Then you could provide a proof that an image which is the same as the "censored", one except for the masked part, has the perceptual hash specified. I don't know if this is technically feasible (but I'd be happy for someone knowledgeable to opine). I also admit that there are secondary concerns, like the possibility of recognising the background image, and this being used by someone to identify the location, or tipping off a criminal.

Probably it would only be appropriate to do this in the case of someone being accused, and maybe then in a way where they couldn't relay the information, since apparently they don't want to make the hash database public.

Also, for the record, I'm spitballing here about infosec. This isn't me volunteering to draw black boxes or be called by anyone's defense.