It is useful to know and we can know from http://www.captcha.net/
"CAPTCHA: Telling Humans and Computers Apart Automatically
A CAPTCHA is a program that protects websites against bots by generating and grading tests that humans can pass but current computer programs cannot."http://www.captcha.net/
And more - "The term CAPTCHA (for Completely Automated Public Turing Test To Tell Computers and Humans Apart) was coined in 2000 by Luis von Ahn, Manuel Blum, Nicholas Hopper and John Langford of Carnegie Mellon University."http://www.captcha.net/
That's why you should decide by yourselves CAPTCHA
or No CAPTCHA
. That is the question.