Lots of people responding to this seem to not understand how perceptual hashing / PhotoDNA works. It's true that they're not cryptographic hashes, but the false positive rate is vanishingly small. Apple claims it's 1 in a trillion [1], but suppose that you don't believe them. Google and Facebook and Microsoft are all using PhotoDNA (or equivalent perceptual hashing schemes) right now. Have you heard of some massive issue with false positives?
The fact of the matter is that unless you possess a photo that exists in the NCMEC database, your photos simply will not be flagged to Apple. Photos of your own kids won't trigger it, nude photos of adults won't trigger it; only photos of already known CSAM content will trigger (and that too, Apple requires a specific threshold of matches before a report is triggered).
The fact of the matter is that unless you possess a photo that exists in the NCMEC database, your photos simply will not be flagged to Apple. Photos of your own kids won't trigger it, nude photos of adults won't trigger it; only photos of already known CSAM content will trigger (and that too, Apple requires a specific threshold of matches before a report is triggered).
[1] "The threshold is selected to provide an extremely low (1 in 1 trillion) probability of incorrectly flagging a given account." Page 4 of https://www.apple.com/child-safety/pdf/CSAM_Detection_Techni...