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, said exclusion comprising filtering the pixel values such that pixel values equal to the excluded at least one element are omitted or replaced by neutral values.