If you put small patches of reflective tape on yourself, you could put a IR, pulsed transmitter on the cam-mount, and 4 detectors.

Then place a 'shadow mask' on a post, with the axis of the post pointing where the camera should be, the mask at the end of it closest to the subject, and 4 sensors at the other end of the post, (farthest from the subject), which are either totally out of the shadow of the mask when the cam is pointed right, or totally in the 'light' being reflected.

If one of the sensors was out of equality with the others, the camera would need to move to reestablish equilibrium.

Brian