Thermal image of a person with glasses, c 1980s.

UNITED KINGDOM - APRIL 10: This image was produced by a heat camera exhibit in the Launch Pad gallery at the Science Museum, London. Everything gives out infra-red radiation, and the warmer the object, the greater the radiation given off. Undetectable to the human eye, infra-red radiation can be picked up by a thermal imaging camera and the resulting image displayed as a 'false colour' picture on a computer screen. Warm objects are represented on the screen by red or yellow, and cool objects by blue or black. (Photo by SSPL/Getty Images)