Here&#x27;s one possible way they <i>could</i> have implemented it:<p>All the recognition happens on the device. Faces are detected, poses are estimated and frontalized, and features are extracted on the iphone. Then, the feature vector is compared to a small gallery of your friends&#x27; features living on the telephone. No upload.<p>That&#x27;s what I hope happens.<p>I don&#x27;t really see much a problem with the above potential strategy, but then again, I wouldn&#x27;t want my recognition model living on my friends&#x27; phones. (One could imagine an attack that tries to extract the images used to train the recognition model given just the model blob...are there any private images there? sounds like a juicy paper!)<p>Or maybe the features are extracted but sent to Facebook, which returns a recognition result. I consider this less trustworthy because Facebook would learn the identity of everyone in any picture I take, even if I choose not to send the full picture to facebook.<p>Or: perhaps faces are detected, but then cropped and the image fragment containing the face is sent to Facebook.<p>Or more Orweillian still, perhaps the entire image is simply sent to Facebook and the recognition happens there.