1. A computer-readable medium carrying one or more sequences of instructions, wherein execution of the one or more sequences of instructions by one or more processors causes the one or more processors to form an object model fitting system based on a set of training images by performing the steps comprising: forming a three-dimensional (3D) object shape model based on the set of training images; forming an object appearance model using the set of training images, wherein the object appearance model comprises a linear combination of a set of object subcomponent appearance models; and forming the object model fitting system comprising an object model comprising the object appearance model and the 3D object shape model.