In the verification setting, here&#x27;s how recognition (could perhaps!) work:<p>- Find the face in the image. This can easily run on a telephone no sweat. Viola and Jones practically solved this problem in 2001.<p>- Find the parts of the face (eyes, nose, mouth), and then warp the face so it looks like it&#x27;s facing right at the camera. A recent paper at CVPR last year was called &quot;Face alignment at 3000 FPS,&quot; so this is also no sweat at all anymore.<p>- Extract the face&#x27;s features. This turns the pixels into a smaller vector representation (maybe a list of 1024 numbers perhaps). This is a bit tricky --- many current systems use convolutional neural networks to do this step, which typically take a lot of compute time. Maybe Facebook could shrink them down to a telephone.<p>- Compare that feature vector to your friends&#x27; vectors. In the verification setting, you know the &quot;feature vectors&quot; of your 500 friends, so you find the Euclidean distance between the image&#x27;s vector and the 500 others. No sweat.<p>- To get a recognition result, just pick the closest vector. Or, if the closest friend is too far away, return &quot;No Match&quot;.<p>There are many ways to build a good face recognizer. This is one of them.<p>This might or might not be what Facebook&#x27;s doing. Last year, they published a paper called &quot;DeepFace&quot; which works essentially this way but with some extra tricks. (The paper is here, but the focus was on comparing to academic state-of-the-art on a strictly academic dataset. It&#x27;s totally marketing &#x2F; PhD recruiting bait. :P I&#x27;m sure their internal system they have now must be far better. <a href="https:&#x2F;&#x2F;research.facebook.com&#x2F;publications&#x2F;480567225376225&#x2F;deepface-closing-the-gap-to-human-level-performance-in-face-verification&#x2F;" rel="nofollow">https:&#x2F;&#x2F;research.facebook.com&#x2F;publications&#x2F;480567225376225&#x2F;d...</a> )<p>The AI and ML people at Facebook are darn smart. I would be impressed (but probably not surprised) if the wizards found some clever way to shrink the pipeline to fit on a phone without too much accuracy loss. So it&#x27;s possible. I have no clue though.