1. A computer implemented method of motion capture, the method comprising: receiving a first frame captured from a real 3D space, the first frame including a first 2D image of a motion capture subject in the real 3D space; deforming a 3D model into a first deformation and placing the deformed 3D model in a virtual 3D space in a first location so that the deformed 3D model corresponds to the first 2D image, the 3D model having at least one deformation constraint that restricts how the 3D model can be deformed; receiving a second frame captured from the real 3D space, the second frame including a second 2D image of the motion capture subject in the real 3D space; tracking 2D changes in the second 2D image relative to the first 2D image; projecting the 2D changes on the virtual 3D space as 3D constraints; and based on the second 2D image, again deforming the 3D model into a second deformation and placing the 3D model in the virtual 3D space in a second location in conformance with the 3D constraints.