This paper presents an approach, using a screen camera closely fixed above the eye to measure and correct the head movement errors, which might free the chin-rest support in eye tracking. The captured screen images, which are warped due to free head movement, could be restored back to the original by applying 3D forward as well as inverse projective mapping. The projective mapping notation and the related processes are described. The preliminary experiment results obtained favored the assumption that head movement errors can be compensated. Eye-tracker free of chin-rest supporting is rather convenient in Human Computer Interaction (HCI) applications.