How to overlay someone (and his/her movements) in a video clip tracking eyes,face,mouth of a 3d character I want to replace/overlay the faces and the bodies of the people that are in a video clip with a series of 3d characters of the same size and shape. 



I set up 8 tracker points for the character's face and eyes in the Movie Clip Editor. The solve camera motion gives a value of 0.6,as you can see below...



After that I have added a camera solver constraint to the head/neck/clavicles bones of the character...



but when I play the animation I see that the mesh does not move correctly according to the movements of the girl that's behind it,rather it breaks. Can someone explains what can I do to fix this ? 



Here you can see a video to better understand what happens. And here you can give a look inside the blender file. thanks.
Well, first of all I would be surprised if this would work at all.
The faces you are tracking are so extremely tiny, that the solver has barely a chance to solve that correctly.
Second, you have a moving camera, so you should solve that first.   

So first track the room and solve the camera for that.
Then, in the objects panel of the clip editor's sidebar, add an object and then place markers on the person's head and try to solve it. 
But as I said, I really don't think it's possible, considering how tiny the persons are in relation to the frame size and how blurry the footage is.