Authenticating a user operating a portable computing device includes causing a sequence of images to be shown on a display, accepting an input selection from the user indicating that a currently displayed image of the sequence of images corresponds to a portion of the user's password, the user's password being known by the portable computing device, correlating the input selection to the currently displayed image, and allowing access to the portable computing device when the input selection and the currently displayed image temporally correspond to the portion of the user's password.