Directly from the link: > ...the system performs on-device matching using a database of known CSAM image hashes provided by NCMEC and other child safety organi

Directly from the link: > ...the system performs on-device matching using a database of known CSAM image hashes provided by NCMEC and other child safety organizations. Apple further transforms this database into an unreadable set of hashes that is securely stored on users’ devices. >... The device creates a cryptographic safety voucher that encodes the match result along with additional encrypted data about the image. This voucher is uploaded to iCloud Photos along with the image.