In this paper, we address the possible effects of video compression on the visual quality of images, that should be considered by person authentication algorithms. We present the block based compression approach which is part of most of the current video compression standards, and two other classes of very low bitrate video compression methods, which are the region-based and model-based methods. Various possible distortions of facial images and sequences caused by these compression algorithms are mainly studied, in order to be considered by person authentication algorithms.