1. A method for identifying an individual, the method comprising: propagating electromagnetic radiation into tissue of the individual; receiving a measured spectral variation in the form of electromagnetic radiation scattered from the tissue of the individual; and comparing the measured spectral variation with a previously stored spectral variation over a predetermined wavelength interval by comparing, at each of a plurality of wavelengths within the predetermined wavelength interval, a property of the measured and previously stored spectral variations that is independent of a presence of other wavelengths; and designating the individual as having an identity associated with the previously stored spectral variation if the measured spectral variation is consistent with the previously stored spectral variation.