What is a captcha ?
Capcha (Completely Automated Public Turingtesttotell Computersand Humans Apart – a fully automated public Turing test to distinguish between computers and people) is a computer test used to determine whether a user of a system is a person or a computer. The term appeared in 2000. The main idea of the test: to offer the user a task that is easily solved by a person, but extremely complex and time consuming for a computer. As of 2013, about 320 million “captcha” are introduced by users all over the world every day.