I remembered bookmarking something I saw a few months ago.
I'm not sure if that project has anything to do with it.
If I ran more than a self-hosted instance that don't allow signups, I probably would look into it more
post:
Fediverse security manager
This is a simple security manager for the Fediverse.
Automatically reports spam in the global timeline by detecting text matches and image MD5 hash values.
https://www.patreon.com/posts/created-spam-for-98757566
https://github.com/nacika-ins/fediverse-security-manager