The intervisibility of two points in a digital grey-scale image array is defined by analogy between the intensity values of the picture elements and surface elevation on topographic surfaces. The distributions of the pairwise visibility (a boolean function) between image points, of the visibility count of the number of points visible from each point, and of the distance of the horizon from each point in selected directions, reveal significant image characteristics. These features allow the classification of images according to type, and subregions according to content and environment. The discriminating power of these features is augmented by the introduction of an observation height that allows shifting emphasis from local to global characteristics.