1) Modern screen test 2) Personal check 3) Reading comprehension test 
A CAPTCHA (an acronym for `Completely Automated Public Turing test to tell Computers and Humans Apart`) is a type of challenge-response test used in computing to determine whether or not the user is human. The term was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas J. Hopper of Carnegie Mellon University and John Langford of IBM. The most.....
Completely automated public Turning test, details ......
Completely Automatic Public Turing Test To Tell Computers and Humans Apart
Completely Automated Public Turing Test to tell Computers and Humans Apart