I don't know the solution for nostr except for relays and image hosts to monitor and remove stuff. Sucks that this is a problem, it's absolutely evil.

It goes way deeper than nostr though. For us, the main thing is that it puts operators in a dicey legal position. This is bad enough, but manageable. But removing CSAM from nostr doesn't solve the root of the problem, which is that it exists — and governments protect and propagate it. I've heard good things about Sound of Freedom. Exposing this stuff is a step towards eradicating it.