No, Clay, I did not say that the flesh RADIATED near IR. (it does, but only a very tiny amount.) The identification system I describe would probably use 940 nm IRLEDs to illuminate the face, and a silicon CCD detector to pick up the images. Or it would use ambient near-IR, perhaps from the sun or a tungsten filament or fluorescent lighting, along with an IR filter to ensure that the CCD camera picked up only the IR bands of interest. It would be easy to check out the results: Put such an IR-passing filter in front of a CCD-based camcorder, and take a picture of somebody.

Incidentally, this simplicity shows the flaw in using this kind of system as an identifier: Since people's faces are usually visible, and can be photographed in the near-IR surreptitiously, it isn't clear how to prevent faking a face which appears to have the same IR signature and pattern.

I remember in a booklet from Kodak on their Ektachrome IR film, there was a picture of a forearm where all the veins were made clearly visible. This film is near infrared (if I remember, the red color on the film corresponds to around 1100 nm). Veins and artery identification might be possible, maybe, since fingerprint identification is possible. A friend of mine developped a quite functionnal algorithm doing just that in the late eighties. OTOH, the blood vessels patterns are probably much more constant, from individual to individual, than fingerprints. Just correct me if I am wrong. JFA PGP 2048 bits key at: http://w3.citenet.net/users/jf_avon ID:C58ADD0D 52 96 45 E8 20 5A 8A 5E F8 7C C8 6F AE FE F8 91 Unsollicited commercial e-mail will be proofread at US165 $/h Any sender of such material will be considered as to have ac- cepted the above mentionned terms.