1. A method, comprising: performing, by one or more computing devices: generating, for a pair of images, a plurality of estimates of relative rotation, focal lengths, and radial distortion according to a plurality of sets of three point-correspondences for the pair of images, where each point-correspondence represents a different feature point that occurs in both of the images; generating a plurality of alignment models for the pair of image according to the plurality of estimates of relative rotation, focal lengths, and radial distortion; and determining which of the plurality of alignment models are to be used for processing the pair of images.