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What is the use of captcha?

Updated: May 16, 2021

Do you fill captchas but not aware why? Here's why do you fill captcha.

Do you always fill Captcha but don't know why do you fill that. Let me tell you.

Let us say that there's a website XYZ where a mobile phone sale will be starting from a particular time, say 11:00 a.m. and if a person is exposed to coding and programming, he/she can easily make a script or a bot to do all the steps required for the sale registration, so a task which will require at least 2-3 minutes for a human being to do will be done within 10 seconds using that script or bot programmed. That means real humans won't be able to purchase that mobile phone on sale. Also, one of the major concerns was that there were lots of spamming bots and scripts that used to corrupt the database of a website by filling in the information in any sort of form using a bot. So in 2003, Luis von Ahn, Manuel Blum, Nicholas J. Hopper, and John Langford came up with a solution that they will put a small box in which scrambled words now well known as Captcha with a noisy background will be given that can not be recognized with a script or a bot.


Captcha stands for Completely Automated Public Turing test to tell Computers and Humans Apart. This makes you fill a scribbled text or identify an image that can be recognized only by human eyes and not by any software, bot or a script. The scripts were unable to bypass this task. Then it being monotonous and inappropriate to fill jumbled meaningless words, a company named "reCaptcha" used the method of OCR which stands for "Optical Character Recognition" scan all the books and hard copies in the world and check that which kind of words were unrecognized by the software, so they started to put up those words in the captcha which were not recognized by these scripts but by humans.

use of captcha

Then in 2009, "Google" bought the company reCaptcha and started innovating these tasks more as it became annoying for people to fill these texts, now google came up with an excellent idea of only checking the tick box stating "I am not a robot". Now it might seem that if one can program a script to fill in the information then one can also program it to check the tick box but when you move your mouse towards the check box, all the information such as your IP address, location, and way of moving the cursor is tracked and sent to Google which by the help of machine learning is recognized whether it was done by a script or a human being. If it thinks 1% of it to be an automated script it will start showing you a set of pictures and ask you to click on the images containing buses, traffic signals, post box etcetera.

why type captcha

So in this way, "captcha" uses a very advanced yet simple technique to differentiate between an automated script and a real human being. So my friend make sure to add "captchas" to your website so that no one can spam your website.

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