My face, as interpreted by my Mac's signature thing. A friend did this with his face a while back, but I didn't know what the "signature thing" was. I discovered it today while I was filling out a pdf form using annotations in Preview, under Tools/Annotate/Signature.

The signature thing uses the camera. You're meant to hold up a signature to it, and it automatically clears away the texture of the paper and makes it transparent except for the black. The algorithm is generally pretty good about not interpreting faces as signatures, but I managed to trick it by standing in front of a white wall, turning my head sideways, and making sure my body was out of view — I then "signed" a document, took a screenshot, and rotated it to be upright.