1. One or more non-transitory computer readable media having computer readable instructions stored thereon for authenticating a user of a computing device that when executed by a processor of the computing device implement instructions for: storing a base image and an overlay image and a particular algebraic result in a memory on the computing device, the base image having a particular base image reference point, and the overlay image having a plurality of numbers that are displayed inside the overlay image; generating a modified base image; generating a modified overlay image; displaying, on a display of the computing device, 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 in response to the input, causing two or more numbers inside the overlay image to align with the particular base image reference point; and in response to alignment of the two or more numbers with the particular base image reference point, applying one or more algebraic operators to the two or more numbers to obtain a result; and successfully authenticating the user if the result equals the particular algebraic result.