1. A method of identifying a particular object from which electromagnetic radiation is emitted and/or reflected at an intensity that fluctuates in accordance with a frequency pattern unique to that object, said method comprising the steps of: (a) detecting electromagnetic radiation that is emitted and/or reflected from an object during normal operation and is not provided as a special identification signal transmitted for the purpose of identifying the object; (b) converting said detected radiation to an electric signal having the same unique frequency pattern as the electromagnetic radiation itself, the frequency pattern of said electrical signal serving as an identifying signature of said object; and (c) using said electrical signal to identify said object.