1. One or more computer-readable media containing a program that is executable by a computer to determine the pose of an object in a given 2D image relative to a 3D model of the object, the program comprising the following actions: matching points of the object in the given image with corresponding points of a base image, wherein each matched point has a corresponding 3D position in the 3D model, the 3D positions being determined by the poses of the images, wherein the pose of the base image is known; calculating the pose of the given image such that projections of 3D positions of matched points of the base image onto the given image coincide approximately with the corresponding matched points of the given image; wherein the calculating comprises: summing the differences between the projections of 3D positions of matched points of the base image onto the given image and the corresponding matched points of the given image; and calculating a pose that minimizes the summed differences.