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Whenever we go to create an account on any website or want to comment on any blog we see scrambled words which we have to type and continue these are CAPTCHAs .

Almost all of us do this earlier while using Internet, but do we aware what is this and why used ? So let’s get information about this.

What is CAPTCHA and How it Works?

A CAPTCHA is a program that can generate and grade tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't:

In simple words, CAPTCHA is the word verification test that only humans can read it and verify it. But any computer generated programs can’t read it and didn’t verify.

Why does CAPTCHA developed?

There are some spam programs which automatically submit comments on blogs, usually for the purpose of raising search engine ranks of some website.

Also Several companies (Yahoo!, Microsoft, etc.) offer free email services. Up until a few years ago, most of these services suffered from a specific type of attack: "bots" that would sign up for thousands of email accounts every minute.

So in need of more security CAPTCHA is developed.

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. At the time, they developed the first CAPTCHA to be used by Yahoo.

Features of CAPTCHA :


CAPTCHAs are mainly used by blogs, websites like Gmail, Yahoo which offer e-mail and other services for which user have to sign-up.

What is CAPTCHA and How it Works?

Jan. 27, 2013 / Posted By - Kiran Patil