We introduce an optimum matched filter for rotation-invariant pattern recognition in scenes with disjoint noise. The optimum filter maximizes the ratio between the correlation-peak intensity and the correlation-output energy; in order to ensure rotation invariance, we assume the filter to take the form of a circular-harmonic function. The performance of this new filter is tested by computer simulations with a variety of natural and artificial backgrounds. The results obtained from these tests show an excellent performance much better than the classical circular-harmonic function (the filter that maximizes the signal-to-noise ratio while maintaining rotation invariance).