We often use this thing (a funny looking image that contains numbers and letters) but may not aware of its technical name. It is called CAPTCHA. The question here is:  What is CAPTCHA ?

If you remember when you create an account in Gmail, Yahoo Mail and at many other  places  it asks you to identify some words which  may be combination of alphabets and digits  having  no meaning displayed in such a way that you have to do effort to identify that word correctly.

For example, given CAPTCHA contains sL88FLwy , but you can see how it is displayed.

CAPTCHA word comes from the word  “capture” and CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart“.

To identify a CAPTCHA is a kind of test in which you have to identify the  given word correctly. It can also  described as a reverse Turing test, used to differentiate a machine from a human.

CAPTCHA is used mainly in registration forms like Gmail, Yahoo and  many more places. In each registration process, CAPTCHA is used to prevent machines to perform actions on behalf of real people. i.e. Aim of CAPTCHA is ‘Telling Humans and Computers Apart’.

This technology is  not only used  in free email registrations but also in
e-commerce transactions, search engine submissions, etc. Some sites also support  ‘Audio CAPTCHA’  that helps you to identify the word by hearing that word and then type it.