[samrolken]

It’s both because it’s a multi-step process.

The image is not fed directly into the hashing function, like taking an MD5 hash of a file or something.

Rather, the image is first evaluated by a neural net that looks at specific visual details, and has been trained to match even if the image has been cropped or anything like that. The results of the neural net evaluation are what is then input for the hashing function.

This is explained in detail in Apple’s documentation they released with the announcement.