>So these photos exist on Apple servers but what they're proposing, if I understand it correctly, is that that data will no longer be protected on their servers. That is, human review will be required in some cases. By definition that means the data can be decrypted. Of course it'll be by (or intended to be by) authorized individuals using a secured, audited system.

Apple has always had the decryption keys for encrypted photos stored in iCloud, so this isn't new. They never claimed that your photos were end-to-end encrypted. I'm not sure how this is a "backdoor" unless you think there's a risk of either something like AES getting broken or Apple storing the keys in a way that's insecure, both of which seem unlikely to me.

>Also, what controls exist on those who have to review the material? What if it's a nude photo of an adult celebrity? How confident are we that someone can't take a snap of that on their own phone and sell it or distribute it online? It doesn't have to be a celebrity either of course.

I'm equally interested in the review process. But while perceptual hash collisions are possible, it seems unlikely that multiple random nude photos on the same device would almost exactly match known CSAM content, which is the threshold for Apple reviewing the content.