Abstract: A method displays an image only to an authorized user by generating a mask image from a data image. The data and mask image are then displayed periodically in an alternating manner on a display device by a select signal. The opening end shutting of an optical shutter device is synchronized to the displaying of the selected images so that only the data image is perceived by the authorized user viewing the display device through the optical shutter device, and a gray image is perceived by an unauthorized user viewing the data and mask images directly.