1. A method of presenting information encoded in an input signal on a visual display adapted to display at least one image frame based on a display drive signal comprising pixel values in a predefined discrete pixel value range, the method comprising: based on an input signal, generating a display drive signal controlling the visual display; based on the display drive signal, computing a checksum of a supervised region of each image frame; and verifying the display drive signal for a given image frame by comparing the checksum, or a value derived therefrom, with the input signal, or a value derived therefrom, wherein the checksum is computed while excluding at least one element in the pixel value range from contributing to the checksum.