Face tracking is one of the difficult things to do in VFX work, I dont know the ultimate technique yet, and there are different situations :
- static markers (there is no deformation in the face)
- deforming face
- the camera (moving or static)
I found that it need more than one camera to do the job (three or more), in my simple case I just used one camera with one reference frame it did the trick, but in production environment you cannt count on such thing.
And put in mind the deference between head tracking and face tracking (in my case although the markers are on the face but its more likely to be a head tracking rather than face).
At the end I got a good result and will develop it more.