It seems that Apple does not need to be a co-conspirator, and that it would be sufficient if someone added ‘malicious’ hashes to the NCMEC database.
Not correct. When enough images to trigger a match are detected apple employees verify the visual derivative to make sure it matches before an alert is generated. They would need to collude.
You’re right, I was thinking about a breach of privacy in general instead of actual legal consequences. (Though the possibility of governments backdooring Apple’s servers to access decrypted files stands, that shouldn’t make a difference with this iCloud-Photos-only spyware)
It isn’t a back door to E2E encryption. It can’t even be used to search for a specific image on a person’s device.
It could be used possibly to find a collection of images that are not CSAM but are disliked by the state, assuming Apple is willing to enter into a conspiracy with NCMEC.