1. Apparatus for checking the integrity of visual display information wherein the visual display information represents an image comprising a plurality of pixels, the apparatus being arranged to: segment at least a part of the image into a plurality of segmented areas compare, for each segmented area, at least one attribute of each pixel therein with a first predetermined value and a second predetermined value; determine, for each segmented area, a number of pixels which meet a first predetermined criteria, wherein a pixel meets the first predetermined criteria based on the at least one attribute being greater than the first predetermined value; determine, for each segmented area, a number of pixels which meet a second predetermined criteria, wherein a pixel meets the second predetermined criteria based on the at least one attribute being less than the second predetermined value; compare, for each segment area, the determined number of pixels which meet the first predetermined criteria with a first reference value; compare, for each segment area, the determined number of pixels which meet the second predetermined criteria with a second reference value; and generate an error signal if the determined number of pixels which meet the first predetermined criteria in one or more segmented areas fails to match the first reference value or if the determined number of pixels which meet the second predetermined criteria in one or more segmented areas fails to match the second reference value.