1. A computer implemented method of motion capture, the method comprising: accessing a 3D model; associating the 3D model with a 2D representation of a subject in a plurality of frames, wherein the plurality of frames captures the subject in a real 3D space; identifying one or more motion vectors derived from a change to the position of 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 position of the 2D representation; and at least one constraint restricting how the 3D model can be deformed, wherein the at least one constraint comprises the one or more motion vectors.