What is CAPTCHA

CAPTCHA:-
CAPTCHA or Captcha (pronounced as cap-ch-uh) which stands for “Completely Automated Public Turing test to tell Computers and Humans Apart” is a type of challenge-response test to ensure that the response is only generated by humans and not by a computer.

In simple words, CAPTCHA is the word verification test that you will come across the end of a sign-up form while signing up for Gmail or Yahoo account. The following image shows the typical samples of CAPTCHA.

source:http://toxylicious.blogspot.com/

Almost every Internet user will have an experience of CAPTCHA in their daily Internet usage, but only a few are aware of what it is and why they are used. So, in this post you will find a detailed information on how CAPTCHA works and why they are used.

What Purpose does CAPTCHA Exactly Serve?

CAPTCPA is mainly used to prevent automated software (bots) from performing actions on behalf of actual humans.

For example, while signing up for a new email account, you will come across a CAPTCHA at the end of the sign-up form so as to ensure that the form is filled out only by a legitimate human and not by any of the automated software or a computer bot. The main goal of CAPTCHA is to put forth a test which is simple and straight forward for any human to answer but for a computer, it is almost impossible to solve.

source:http://www.captcha.net/

What is the Need to Create a Test that Can Tell Computers and Humans Apart?

For many, the CAPTCHA may seem to be silly and annoying, but in fact it has the ability to protect systems from malicious attacks where people try to game the system. Attackers can make use of the automated software to generate a huge quantity of requests thereby causing a high load on the target server. This could lead to a degrade the quality of service of a given system, either due to abuse or resource expenditure. This can affect millions of legitimate users and their requests. CAPTCHAs can be deployed to protect systems that are vulnerable to email spam, such as the services from Gmail, Yahoo and Hotmail.