Systems and methods are disclosed for computer-based user authentication to prove user identity or to approve access to a resource such as a computer system, in which a user performs a set of actions on at least one verification image on a display screen. Users are authenticated by a computer comparing the set of actions against a key definition for the verification image. The set of actions may include selecting at least one target location on the image, selecting target locations in a selected order, selecting the target locations with a selected pattern, selecting at least one overlay with which to cover a one target location, superimposing a target location with a selected overlay, covering the target locations with overlays in a selected superimposing order; and covering the target locations with overlays in a selected superimposing pattern.