A 2-D position-sensitive photon-counting detector is used in an optical random number generator in which the locations of detected photoevents provide the random numbers. The spatial distribution of photoevent locations is dictated by imaging a control object onto the detector. An iterative calibration procedure is used to determine the brightness distribution of the control object. Two control objects were examined-film and a video monitor. With both control objects, the performance of the optical random number generator approached that of pseudorandom number generators.