1. A system for verifying the purported identity of a target individual comprising: an enrollment database including tissue optical spectral data collected from at least one enrolled persons, said enrolled persons optical spectral data having a plurality of measurement values; means for obtaining at least one tissue optical spectral data and purported identity from said target individual, said target individual's optical spectral data having a plurality of measurement values; means for comparing said target individual optical spectral data and said enrolled persons optical spectral data, said enrolled person optical spectra corresponding to the purported identity of the target individual, said comparison providing a measure of the degree of similarity between said target optical spectral data and said enrolled person's spectral data; and means for positively verifying said target individual's identity by confirming that said target individual's measure of spectral similarity is at least as similar as an established threshold value.