This paper surveys the visual distortions introduced by a compression scheme into the reconstruction of a video sequence. Specifically, the paper will concentrate on systems utilizing motion compensation (MC), differential pulse code modulation (DPCM), and the discrete cosine transform (DCT). Such systems are exemplified by the CCITT H.261 and MPEG standards. In addition to the artifacts that have already been widely considered, such as `blocking' and `mosquito' effects, new classifications of artifacts will be presented. A concise characterization and demonstration of each artifact will be provided. This will include the specification of the distribution of the artifact within the reconstructed frames, and its correlation with the local spatial/temporal features within the sequence. Also noted will be the specific causes of the artifacts, with relation to the MC/DPCM/DCT components. Since the human visual system is, typically, the final judge of the quality of the reconstructed sequence, it is also important to note the level of severity of the artifacts that make the artifacts visually noticeable.