[GrantS]

Yes, the results of all the learning can be saved in a compact form which is efficiently run on the device. Apple just yesterday unveiled their neural network API [1] which they are presumably using for these tasks. The description states: "BNNS supports implementation and operation of neural networks for inference, using input data previously derived from training. BNNS does not do training, however. Its purpose is to provide very high performance inference on already trained neural networks."

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...