CAPTCHA- A Computer Program

CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Human Apart) is a system that is used to make sure that it’s a human being but not a machine. The person may be asked to type in a series of letters or numbers, or to complete a simple game. It’s a  computer program or system intended to distinguish human from machine input, typically as a way of avoid spam and automated extraction of data from websites.

Luis Von Ahn , Manuel Blum, Nicholas J. Hopper and John Langford coined the term CAPTCHA  in the year 2003. The reason behind that websites implement CAPTCHA because of spam. Those letters of CAPTCHA is a way to check if it’s the real human being or a computer program attempting to spam the site.

“We are in that age of machines , where we have to prove machines that we are not machines.” -Ritveak

When we browse the internet, we face CAPTCHAs, the twisted words which stops or enables the entire websites.  CAPTCHAs blocks the spam. It tests effectively whether the person is human or BOT or machines. In BOTs cannot recognize each letter alone.

CAPTCHA helps to protect our websites or blogs from comment spams as bloggers receive number of spam comments each day. It also helps search engine to prevent crawling the spam content that may be harmful for keeping database safe.



reCAPTCHA is another interesting application of CAPTCHA. Among several projects, one of them is converting books to the ebook version i.e scanning the books. reCAPTCHA solved this problem. Its hosted by Google. It supports two version , one is to enter some text and another is to checkbox to choose “I’m not a robot”. It’s a type of CAPTCHA , its easier for human and relatively difficult for BOTs to crack.

There are different types of CAPTCHA

1. Standard CAPTCHA

reCAPTCHAIn this type of CAPTCHA a user is shown with a scrambled word which the user has to enter in the box or with audio option if the user is visually impaired.

2. Image recognization CAPTCHA

image recognizationIn this type of CAPTCHA a user is provided with set of pictures where the user needs to identify the picture.

3. Maths solving CAPTCHA

maths solving In this CAPTCHA a user needs to solve a simple math problem like addition or subtraction.



This is difficult form of  CAPTCHA where an image is shown in 3D form and the user has to recognize it. It is also called as Super CAPTCHA.

5. Ad-injected CAPTCHA


If a user is spending most of the time over a CAPTCHA then the user solves the CAPTCHA with an Ad . This helps website to earn .

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