"Wearing face masks that adequately cover the mouth and nose causes the error rate of some of the most widely used facial recognition algorithms to spike to between 5 percent and 50 percent... Black masks were more likely to cause errors than blue masks, and the more of the nose covered by the mask, the harder the algorithms found it to identify the face."

Picking out faces in a crowd is harder because you can’t control the angle or lighting on the face and the resolution is generally reduced.