How to teach Envision faces?

In the Envision app, take about 5-10 pictures in different angles of the person's face you want Envision to recognize. Save the images and wait a couple of seconds for Envision crunch its brain. Once Envision is all up-to-date on the person's face, you can test it by using Scene Description. The faces you have taught Envision, will be spoken out when you scan the person's face.