Abstract: An image registration system for registering multiple images on a screen is disclosed. A registration pattern is projected on the screen along with the image to be registered and in a fixed position in that image. A sensor apparatus for each image, having three photodetectors disposed in a right angle relationship is mounted on the screen at a predetermined location for determining the position of the registration pattern on the screen. The position of the registration pattern on the screen is determined by comparing the outputs of the three photodetectors. Difference signals are produced by the comparisons and are used to reposition the projected image to bring it into registration. The sensor apparatus are disposed so that when the registration patterns are in register with them, the images are in register with each other.