1. A computer implemented method of motion capture, the method comprising: accessing a 3D model of a subject; associating the 3D model of the subject with a 2D representation of the subject in a plurality of frames; identifying a change to the 2D representation of the subject between two or more of the plurality of frames; and deforming the 3D model in a virtual 3D space, wherein the deforming is based on: the identified change to the 2D representation; and at least one constraint restricting how the 3D model can be deformed.