The invention provides an apparatus and method for checking the integrity of visual display information and has particular application to checking images displayed in an automotive vehicle, such images containing safety critical information. The image intensity is checked only to an extent commensurate with a human being able to interpret its correct meaning. Hence, images which are defective in some way yet still recognisable by the human eye are not classified as failures. In one embodiment, a part of the image containing safety critical information is segmented into smaller areas and the luminance of pixels in each segmented area is compared with a threshold brightness level and a threshold darkness level. A histogram for each area is generated and compared with a reference.