1. An apparatus for identifying an individual comprising: radiation source means adapted to illuminate a region of the skin of an individual which is substantially opaque to visible radiation but substantially transparent to radiation from said source, means for detecting radiation from said source means reflected from the individual and sensitive to lateral variations and intensities of said reflected radiation so as to detect the arrangement of subcutaneous blood vessels in said region of the skin, wherein said means for detecting includes transducer means for generating a signal indicative of the variation of the arrangement of subcutaneous blood vessels; and comparator means for comparing said signal with a reference signal characteristic of the individual.