1. A computer-implemented method of calculating pose or shape of an articulated or deformable entity comprising: receiving at least one image of the entity; accessing a model of a class of articulated or deformable entities of which the imaged entity is a member, the model comprising a plurality of parameters specifying the pose or shape of the model; using the image to access a plurality of candidate correspondences between image elements of the received image and model points which are locations on or in the model; carrying out an optimization process to find values of the parameters specifying the pose or shape of the model which agrees with the received image; and where the optimization is influenced by at least some of the candidate correspondences.