A clever method of image registration is presented which is based on the number of sign changes in the difference image of the two source images being registered. In the presence of noise, the number of sign changes is maximum when the sources are in registration. If the images are not noisy, an artificial noise can be added. The method is compared with three known methods of registration: correlation coefficient, correlation function, and sum of absolute value of the differences. The results (for medical image cases) appear excellent. The paper would have benefited by comparison to phase shift correlation (see [1]).