1. One or more computer-readable storage devices storing computer-executable instructions which when executed by a computer cause the computer to perform a method, the method comprising: receiving an image of a user of a device; identifying one or more facial descriptors of the user from the received image; and evaluating whether the one or more identified facial descriptors of the user match one or more facial descriptors of a previous user extracted from multiple previously captured images of the previous user, the multiple previously captured images of the previous user being captured under different light sources, at least one image of the previous user being of the previous user illuminated by a low-light source, the evaluating comprising cross verifying the received images against at least one image of a non-user, the cross verifying comprising computing a distance between the received image and the at least one image of a non-user, and determining if the distance between the received image and the at least one image of a non-user is greater than a non-user image threshold value.