A method to drive a pixelated display of an electronic device arranged in sight of a user of the device. The method includes receiving a signal that encodes a display image, and controlling the pixelated display based on the signal to form the display image in addition to a latent image, the latent image being configured to illuminate an eye of the user with light of such characteristics as to be unnoticed by the user, but to reveal an orientation of the eye on reflection into a machine-vision system.