This is so crazy and I have no idea how we can protect nostr from it if any reference is illegal and only centralized institutions are allowed to deal with it at all. Hashes sound like a reasonable thing to collect upon deleting stuff as it could be used to avoid displaying it to other users. Sadly hashes can indeed lead to discovery in content-addressable systems and of course, marking stuff as CP is a pretty sure way to keep people from opening it even if it's not actually CP.