I think you're probably wildly overoptimistic about the ratio of police officers to private nudes.

No government really wants to be fully enforcing all their own laws, just because it's way too expensive to hire that many cops. I think the closest anyone got was the Stasi, and they had a lot of "volunteers": https://en.wikipedia.org/wiki/Unofficial_collaborator#Other_...

I think a more realistic system would be hashing images and comparing them to known CSAM in some database.

I think Apple was going to implement something like this a few years ago before scrapping it.