A few options:
Filter public relays from global. Public relays will always have garbage like this just from trolls and feds.
If people want to be a part of the solution, i recommend this yesterday:
nostr:note1thc256k4rycz9kh79ufw2zhss3hqwkwl7us4qrv0wh6uy2ph6t9qm2f2fj
If clients had ways of alerting image hosts of the content they are hosting, they might have more pressure to actually fix the problem by screening uploads.