Google photos only groups similar faces and requires the user to assign a name to that group. Apple could presumably perform the grouping in the cloud and relegate the association of the group with an identity to the user's device.
The data set to learn from probably can be gathered from stock photos or other open source images, but can that learning be saved down to phone and used to compare against, or would it be too big?
If too big, does that mean characteristics of an image would be computed on the phone sent to the cloud compared and the results sent back?
So they're really saying that no data leaves the device for either object or face recognition at classification time. Now, whether they are using iCloud-stored photos (which the user has already agreed to share) for training, I don't know, and any privacy issues would still be important at that point.
[1] https://developer.apple.com/reference/accelerate/1912851-bnn...