You might have often encountered a message saying “Enter the both words below, separated by a space” or “Type the two words present in the box” or many other such messages.
Why are these required??
It’s a program called CAPTCHA, that can generate and grade tests that humans can pass but current computer programs cannot.
CAPTCHA stands for Completely Automated Public Turing Test To Tell Computers and Humans Apart.
Complete details-
http://computer.howstuffworks.com/captcha.htm
