Before an image is stored in iCloud Photos, Apple said an on-device matching process is performed for that image against the unreadable set of known CSAM hashes. If there is a match, the device creates a cryptographic safety voucher. This voucher is uploaded to iCloud Photos along with the image, and once an undisclosed threshold of matches is exceeded, Apple is able to interpret the contents of the vouchers for CSAM matches. Apple then manually reviews each report to confirm there is a match, disables the user's iCloud account, and sends a report to NCMEC. Apple is not sharing what its exact threshold is, but ensures an "extremely high level of accuracy" that accounts are not incorrectly flagged.