What is CAPTCHA & how does it work?

February 19, 2021
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What is CAPTCHA? How does it work?

Are you a robot? Maybe you are a robot. Even if you are a robot, you can still read this article. Because, before we read the article, we didn’t ask you to prove that you are a human or a robot. Can’t find anyone who use internet but doesn’t see the words “I am not a robot”. So CAPTCHA is not a new word for regular internet users. Nowadays, CAPTCHA is found on almost all websites. A lot of the time just before you can comment somewhere or log in to your account, a popup window like the one below is given in front of you. Through this window you have to prove yourself as a human not a robot. Today we will learn about this CAPTCHA and how it works.


What does CAPTCHA mean?

CAPTCHA is not an English word. This is just an illustration. CAPTCHA is a word or shot form of the first letter of a few English words. The term “CAPTCHA” is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. That is, CAPTCHA is the process of automatically verifying the difference between a human and a computer. A system through CAPTCHA determines whether a person is involved in a process, or whether the work is being done by a spam robot. The CAPTCHA process involves looking at different types of numbers, texts, or information that can only be input by humans. Generally, no computer controlled system can fill CAPTCHA.

 (CAPTCHA) History of Creation

CAPTCHA is used on various websites that verify whether the user is a robot. The father of CAPTCHA is Luis von Ahn. The term CAPTCHA was first used in 2000 by computer scientists at Carnegie Mellon University. The first CAPTCHA was used to verify online polls. In 1999, Slash Dot created a survey asking visitors to choose the best programmed undergraduate school for computer science. Carnegie Mellon and MIT students created an automated program called bot for repeated voting at their school. However, so far no capture has been named. Capture was officially named in 2003.

It is most commonly used on sites like Yahoo Mail or Gmail, where people can create free accounts. It is hinders the process of creating spam email accounts on these sites. CAPTCHA is also used to prevent spammed messages and comments on web pages and blogs. It does not prevent cyber bullying, but it does prevent bots from posting messages automatically.

How does CAPTCHA work?

CAPTCHA was invented primarily to block comments posted by spammed software. Capture work is a lot like a Turing test. Which give user some small work, which is usually not possible for any software or Robot. The most common form of CAPTCHA is an image with some distorted letters and numbers. There is also a widespread use of CAPTCHAs that have to separate specific thematic sections from a single image.

The Internet and computers basically use coding languages. Computers cannot understand human language without coding language, because human language is made up of wonderful and complex rules. Capture words or letters are sometimes so disjointed that it is difficult for people to understand. This is why many sites have the opportunity to change CAPTCHAs or listen to audio.

CAPTCHA Requirements:

CAPTCHA was originally created to prevent spamming, although CAPTCHA is now being used for many more purposes. But how does it is prevent spamming? Suppose a new popular movie has been released today. As it is a new movie, more people than usual will be interested to go to the cinema hall and watch the movie on the first day. As a result, the demand for movie tickets on the first day will be higher than usual.

Now with this opportunity a computer programmer will create an intelligent program with the help of which he will buy all the tickets online from the first day alone. To do this he must need a powerful bot or program, because he can never do this alone. With the help of this bot or program he will buy all the tickets in advance and then start black marketing. As the tickets are out of stock and the demand for tickets is high, he will be able to sell these tickets at a higher price than the price he bought himself.

Captures are needed to prevent such illegal activities. To prevent this type of work, the server needs to understand whether the device that is accessing the server is being operated by a real person or a bot created by a programmer. It will be possible to stop this whole process if you understand it in advance. For that, just before accessing the server, it is necessary to give some tasks which are very easy for humans but very difficult for computers or robots.

Effectiveness of CAPTCHA

Unfortunately, as technology and malicious hackers improve, so do their scams. Although CAPTCHAs are much more secure, cybercriminals are now incorporating CAPTCHAs into their fake or fraudulent websites to make their scams more credible.


CAPTCHA is used in most websites and blogs to protect websites and users. CAPTCHA is used in many cases. The following are some of the fields-

  • Protect email services from fraudsters
  • Protect website registration system
  • Protect online polling
  • Protect from spam mail / junk mail
  • Prevent online comment spamming

In fact, it is the same CAPTCHA as before. But it is much smarter and more intelligent than before. When Google saw that the previous method did not work well, they thought it would be easier for humans and more difficult for robots. They think a lot and get a good way. Then they thought that instead of text in the CAPTCHA they would give some small pictures and everyone would be asked to find and mark a specific object from those pictures. For example, you may be given some small pictures and asked to mark the road signs from those pictures or from a big picture to the part of the picture that have a car in them. Unless you are able to do this properly, you will not be allowed to access the site.

Currently this CAPTCHA system is the most used and the most popular. Again many times you will not even need to fill this CAPTCHA. All you have to do is click on CAPTCHA and after a while you are approved as a human without doing anything. How does it work? This method is even smarter. Behind this method is Google’s extraordinarily powerful artificial intelligence. In this method, when you click on Capture, your activity is tracked. Actions include your mouse cursor movement, your browser’s cookies, your IP address, your overall browsing habit, and much more that Google has kept secret. Mainly your mouse cursor movement and your browser data checked.

If you are human, your mouse cursor movement will not be specific. This means that your mouse cursor will continue to move in different directions. But if you are a robot, your mouse cursor will go straight to the capture and click. This is the only way to understand whether you are a human or a robot. Once you are sure that you are human, you will be allowed to go without any task. But even after seeing it and noticing your browsing habit, if there is any doubt, you will be given the task of marking that picture.

Do you like CAPTCHA? Let us know your comments or thoughts about CAPTCHA in the comments section.

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