1. A computer-readable storage device comprising instructions for causing at least one processor of a computing device to perform operations comprising: capturing, by an image capture device coupled to the computing device, an image of a face of a user; detecting whether a distance between the computing device and an object represented by at least a portion of the image is less than a threshold distance; and when the detected distance is less than a threshold distance, denying authentication of the user with respect to accessing one or more functionalities controlled by the computing device.