Abstract. In video surveillance, the faces of interest are often of small size. Image resolution is an important factor affecting face recognition by human and computer. In this paper, we study the face recognition performance using different image resolutions. For automatic face recognition, a low resolution bound is found through experiments. We use an eigentransformation based hallucination method to improve the image resolution. The hallucinated face images are not only much helpful for recognition by human, but also make the automatic recognition procedure easier, since they emphasize the face difference by adding some high frequency details.