What are CAPTCHAs? How Does it Work?

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You must have seen some weird distorted images and/or a checkbox reading, “I’m not a robot” while filling a form online or shopping for some stuff. That thing is called CAPTCHA and CAPTCHAs are used widely in shopping websites, sign-up pages, booking tickets online, and some other spaces too.


Well you must be wondering why is that thing in place as it does not seem of quite useful and is often a bit confusing and irritating. In this article we will be learning a bit about what is CAPTCHA and how does it work and why do we need it at all.

What is CAPTCHA?

CAPTCHA is an acronym that stands for Completely Automated Public Turing Test to tell Computer and Human Apart. So as the full form suggests, CAPTCHA does pretty much the same thing, it is a Turing test that is in place to detect the humans visiting a site apart from bots.

Turing test is a test to differentiate between Humans and computers and they are designed in such a way that it is almost impossible for a computer to pass the test while humans could solve the puzzle in the test fairly easily.

Why Do We Need CAPTCHA?

To understand why we need CAPTCHA, let us take an example. Let’s say you made a website that requires users to sign up and I am a person who hates you a lot for no reason. So, what I can do is that I can design a script or a bot that would automatically fill all the required credentials on your website for sign up and run the script.

And BOOM! You have thousands of sign-ups that are of no use and are spams for your website. So, to solve this problem, there comes CAPTCHA for rescue.

If you will use CAPTCHA on your website then it will be impossible for a script to bypass that and the script or bot won’t be able to progress to the next step and this will stop the spam accounts being created on your site.

How Does CAPTCHA Work?

So, this is what CAPTCHA does, it protects spamming on websites. It is very hard to bypass a CAPTCHA code by a computer as computers can read and recognize normal text, speech, and image patterns but it is very impossible for them to recognize the same if they are a bit distorted.

To give you a little background, CAPTCHAs have an 80% success rate for humans and a 0.01% success rate for computers. That is why companies for online shopping, ticket booking, forms by universities, and sites that require sign-up for use CAPTCHA as it stops unnecessary spamming.


Different Types of CAPTCHAs

There are quite different types of CAPTCHAs that you would see online while doing various stuff and some of the most seen are:

Distorted Letters and Numbers

You would generally see them online on sites that offer a form to fill up and these are distorted letters and numbers arranged in a very random pattern and you would need to type them to progress to the next step.


Mathematical Calculations or a General Question

This CAPTCHAs can be seen on sites that require you to login or just go to new webpage and are not very sophisticated.

Audio CAPTCHAs  

These are the same as the distorted numbers and alphabets but in audio format and have a noise in the background which can only be understood by humans.




This is a new adaptation by Google that is fairly easy to do and less time-consuming. It just requires you to click on a box that reads “I’m not a robot”. You would be wondering what is so hard in it? Can’t a computer bot do it easily?

Well the reCAPTCHA tracks mouse movement which is very random in the case of humans and very sorted and straight in case of computers and that is easily detectable. It also tracks IP address on cookies to see if everything is in place and if something is suspicious, you will be redirected to a new type of verification that would want you to sort out some particular types of images from a group of images.

So, this was all about CAPTCHAs and How do they work. Do let us know about more stuff related to CAPTCHAs in the comments.

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