1. One or more non-transitory computer readable media having computer readable instructions stored thereon for 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 base image reference point, and the overlay image having an overlay image reference point, which when executed by a processor direct the computing device to: generating a modified base image; generating a modified overlay image; displaying, on a display, the modified base image overlaid by the modified overlay image, wherein displaying includes varying at least one of a position of the base image reference point on the display and a position of the overlay image reference point on the display relative to a previous displaying of the base image and the overlay image; receiving an input causing 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; and in response to the alignment, indicating positive authentication.