What is CAPTCHA Verification?

There are times when before registering on some social media, filling up a form or surfing different websites on the internet, a ‘captcha verification’ window pops up. The user is supposed to either copy down some distorted text, solve a mathematical equation or sometimes is required to identify an object from a set of multiple images. This verification window is called a Captcha test.

The article below contains more about what exactly captcha means? what is the purpose of the Captcha code? and some of the other related queries too.

What is Captcha? (Examples)
What is Captcha? (Examples)

What is Captcha?

CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. As the name suggests it is a test that determines whether the user is a real human or a machine or bot.

Machines are unable to perform these tasks with greater accuracy than humans. For example, the machine can not read the distorted text, which can be easily understood by humans. Hence, the system uses these tasks to predict whether the user is a real human or just a machine/spammy bot/automated program. Distorted image Captcha

What is the use of CAPTCHAs?

Since the earliest use of the internet, certain users are trying to make text hard to be detected by machines for various benefits. One such group of users was hackers. The automated filters used to monitor and remove the posts about sensitive topics based on certain sensitive keywords. Thus the users started replacing the sensitive words with look-alike characters to bypass such automated filters. For example, ‘sensitive’ could be replaced by ’53n5171v3′. This technique later became known as Leetspeak.

In 1999, Slashdot hosted an online poll for the best school for the computer science program. Many students from reputed schools used bots and automated programs to illegitimately vote in favor of their schools. Hence they introduced Captcha in this poll to prevent illegitimate voting.

In 2000, idrive.com started to protect its signup page with a CAPTCHA code. In 2001, PayPal also started using this technique to prevent frauds in which they asked the users to retype a distorted text that bots have difficulty in recognizing. PayPal co-founder Max Levchin helped commercialize this use.

PayPal Captcha Verification
PayPal Captcha Verification

reCaptcha by Google is a popular use of Captcha technology introduced in 2009.

What is reCaptcha?

ReCaptcha is a service offered by Google which can be used to protect one’s website from spammy bots and automated programs.

History (early use of reCaptcha):

The original slogan for reCaptcha was “Stop Spam. Read Books.”


Recaptcha used Captcha technology to check whether the user is a real human or bot. The reCaptcha displayed two words. One of these words was a normal captcha code to which the system knew the answer to and thus used to verify the user. Another word was an ‘unknown’ word. The words that the system couldn’t recognize in the Book Digitization process were the ‘unknown words’.

Book Digitization process
Book Digitization process

Recaptcha contained the words left unknown during the book digitization process. In the above picture, OCR couldn’t identify ‘between’. Hence, in the reCaptcha, ‘between’ is the word unknown to the system and ‘upon’ is the known word. Hence, the word ‘upon’ checks, if the user is machine or human, and if it’s a human, the system stores the word ‘between’ as entered by the user. In this way, Google introduced the concept of reCaptchas to make productive use of people’s time and effort.

Currently :

After the introduction of a new plugin in 2004, the new slogan of reCaptcha is – “Easy on Humans, Hard on Bots.”

reCaptcha v3
ReCaptcha v3

In 2014, reCAPTCHA started to implement the behavioral analysis of the browser’s interactions with the CAPTCHA. It checked whether the user was a real human or a bot/program without displaying the CAPTCHA. This technique relies on the use of Google cookies that are at least a few weeks old.

How safe are Captchas?

Captchas were originally introduced for the safety and security of websites but they are not 100 percent secure. Captchas can bring many complications to the site’s privacy policy. They also have the potential to drive the customers away.

Some of the alternatives other than using Captchas for stopping spam bots are –

  • Allowing users to identify themselves by connecting an account they already have for example a FaceBook account, email, etc.
  • Adding additional fields that would be invisible to human users via CSS property visibility: hidden. Hence, the system identifies the user as a bot if these invisible fields are filled.

In case you’re wondering how can you learn more about captchas and other related concepts, UDEMY has a lot of free and paid courses regarding that. Here’s how you can get the paid ones for free- FREE UDEMY COURSES.

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