1. A method comprising: receiving, by a computing device, a first image and a second image; detecting, by the computing device, a facial gesture at least in part by determining whether a difference between the first image and the second image indicates a facial gesture; selecting, based at least in part on the detected facial gesture, the first image and the second image from among a plurality of images that includes at least the first image, the second image, and a third image; subsequent to selecting the first image and the second image, determining, by the computing device, whether the first image and the second image are associated with a consistent identity, based at least in part on a similarity between the first image and the second image; and determining, based at least in part on detecting the facial gesture and on determining whether the first image and the second image are associated with the consistent identity, whether to deny authentication with respect to accessing one or more functionalities controlled by the computing device.