1. One or more computer readable media having computer readable instructions stored thereon that when executed by a processor implement a method of authenticating a user of a computing device, the computing device having a memory storing a base image and an overlay image, the base image having a pre-selected base image reference point, and the overlay image having a pre-selected overlay image reference point, the method comprising: generating a modified base image; generating a modified overlay image; displaying, on a display, the modified base image overlaid by the modified overlay image; receiving an input for moving one of the modified base image and the modified overlay image; moving the one of the modified base image and the modified overlay image if a criterion for movement of the one of the modified base image and the modified overlay image is met; and in response to alignment of the base image reference point on the modified base image with the overlay image reference point on the modified overlay image at a point on the display after the moving, indicating positive authentication.