True, it’s hash-like in that the comparison is using some mathematic representation of the source material. It was intended to be a little fuzzy so it would still catch minor alterations like cropping, watermarks, rendering to a new format, etc…

The example I heard of was someone that was using an app for a remote doctors appointment. The doctor requested photos of the issue, a rash in the genital area of a minor, supposedly one included an adult hand touching the area involved. That photo ended up in Google’s cloud service where it was flagged, reported to law enforcement, and that users while Google account was frozen. The investigation quickly confirmed the innocence of the photo, and provided official documentation of such, but last I heard Google would not release the account.