Motion relative to a surface is addressed. Image flow can be caused either by motion of objects in the world or by motion of the eye through the world. If knowledge exists of eye motion, dense range maps can be computed locally for all stationary object pixels. Range from image flow can be computed either by gradient methods or by correlation methods. The former are simple but subject to quantization noise. The latter are complex but much more accurate. If eye rotation is known, image flow due to eye translation can be separated from flow due to rotation, and moving objects can be segmented from a stationary background. Topics discussed include the equations of image motion on the egosphere, the method for determining optical flow of B.K.P. Horn and B.G. Schunck (1981), cross correlation, image enhancement by scanning, obstacle avoidance navigation and the temporal integration of image flow. >