In accordance with one embodiment, a method of determining a transformation between a first image and a second image includes acts of, for at least one region in the first image, determining a corresponding region in the second image as a function of a transformation parameter and determining a similarity function as a function of the transformation parameter between the region in the first image and the corresponding region in the second image. In one embodiment, the method further includes acts of determining a similarity function between the first image and the second image using the similarity function for the at least one region, and determining a value of the transformation parameter, wherein the value substantially optimizes the similarity function between the first image and the second image.