In identifying skeletal remains, forensic anthropologists can determine whether or not the skeleton is human, age at death, sex, race, stature, number of remains, and wounds. Also, some anthropologists can reconstruct the appearance of an individual from the skull either by building up appropriate thicknesses of clay over specific landmarks where those thicknesses have been measured in flesh-covered cadavers or by more direct photographic techniques. Some forensic anthropologists can determine blood type and even electrophoretic patterns that can identify an individual's blood specificity that equals or surpasses fingerprint identification, if fresh whole blood is available. Physical anthropologists study hair form and color as variants within and between living populations and can often determine the major racial population of a person or skeleton from the general structure of the hair. Forensic anthropologists can also identify footprints where no dermatoglyphic ridge patterns are discernible, notably where sock-clad feet have left bloody prints. For purposes of identification, some forensic anthropologists have developed techniques for comparing photographs of unknown subjects with those whose subjects can be identified. Twelve references are listed.