How to train Face ID to recognize weird facial expressionsFace ID uses machine learning to familiarize itself with your various facial changes. You can even train it to recognize your scrunched up face!
To simplify a very complex process; Face ID captures your facial structure and uses it to identify you and then unlock your iPhone. It also learns the ways in which your face changes over time and throughout the day. If, for example, your eyes are really puffy in the morning, Face ID learns that its still you, but with a slight change in your "expression." iMore Editor in Chief, Rene Ritchie, explained how Face ID uses machine learning to recognize minor changes to your face.
Face ID may also store, for a limited time, the math from successful unlock attempts and even from unsuccessful unlock attempts where you immediately followed up by entering the passcode. That's to help the system keep pace with changes to your face or look that might accrue over time, even the more dramatic ones. After it's used the data to augment a limited numbe...
Source:
How to train Face ID to recognize weird facial expressions
