1. A method of controlling access to an electronic device, the method comprising: generating a modified first image from a first image, wherein the first image and the modified first image include a first reference portion; generating a modified second image from a second image, wherein the second image and the modified second image include a second reference portion; displaying, on a display of the electronic device, the modified first image overlaid by the modified second image; automatically changing the color of the first reference portion of the modified first image or the second reference portion of the modified second image; and authenticating access to the electronic device in response to substantial alignment of the first reference portion in the modified first image with the second reference portion in the modified second image and in response to receiving input selecting a color for the first reference portion of the modified first image or the second reference portion of the modified second image which matches a designated color.