Let me get this straight- the iPhone will now scan your iCloud account and compute hashes for images. These hashes are then compared against a known database of child abuse images. When a certain threshold of "hits" is reached then steps are taken to notify authorities?

There seems to be little chance of false positives here. I keep seeing references to machine learning algos and that's not what they are doing at all. I do still lament losing yet more control though. A device that I buy should not be working for somebody else, for better or worse.

CSAM is not new and is already in widespread use. The difference here just seems to be that your device itself will sell you out.

Edit: Follow up question- They run this on images before they are uploaded to iCloud. Why has Apple chosen to do this on-device rather than just run it in iCloud? They say for privacy reasons:

'Apple’s method of detecting known CSAM is designed with user privacy in mind.'