This article proposes a back-projection technique for the modeling of 3-D human motion that performs camera calibration using the multiple video sequences obtained. This technique calculates an affine camera matrix by the factorization method, and performs back-projection under the affine camera model. The proposed technique needs neither a 3-D camera calibration tool nor markers for shape recovery, and can recover human motion from silhouette images. We also propose a shadow detector and eliminator using color information and normalized cross correlation for the robust extraction and elimination of shadows. Experimental results show the effectiveness of the proposed technique.