1. A method comprising: receiving, from an image capture device coupled to a computing device, a first image of a face of a user, and a second image of the face of the user; identifying at least one facial landmark in the first image and at least one corresponding facial landmark in the second image; extracting, by the computing device, a first sub-image from the first image, wherein the first sub-image represents a portion of the first image, and wherein the first sub-image includes a representation of the at least one facial landmark; extracting, by the computing device, a second sub-image from the second image, wherein the second sub-image represents a portion of the second image, and wherein the second sub-image includes a representation of the at least one corresponding facial landmark; detecting a facial gesture by determining, by the computing device, whether a sufficient difference exists between the second sub-image and the first sub-image to indicate the facial gesture; determining, by the computing device, whether the first image of the face of the user and the second image of the face of the user are associated with a consistent user identity, based at least in part on determining whether a sufficient similarity exists between the first image of the face of the user and the second image of the face of the user; and determining, based at least in part on detecting the facial gesture and on determining whether the first image of the face of the user and the second image of the face of the user are associated with the consistent user identity, whether to deny authentication to the user with respect to accessing one or more functionalities controlled by the computing device.