12. The method of claim 11 , wherein said reference challenge items are ranked and sorted according to a score provided by said human test subjects, and further including a step: presenting said one of said set of reference challenge items based on said score.
11. A method of implementing a CAPTCHA (Completely Automatic Public Turing Test To Tell Humans And Computers Apart) to identify a source of data input to a computing system comprising: a) using a set of human test subjects to identify whether a reference challenge item was vocalized by a human or a computer; b) training the computing system with samples of human voices and computer synthesized voices articulating a set of the reference challenge items; c) receiving a speech utterance from an entity related to one of said set of reference challenge items; d) determining with the trained computer system whether said speech utterance was vocalized by a machine or a human.