CAPTCHA: What is it and why is it used?

Many people ask the question what is the meaning of captcha? CAPTCHA is a computer tool that helps us limit spam generated by bots. You may have used it when you last registered for a new service or when sending a message via a contact form.

CAPTCHA: what is captcha and how does it work?

The acronym CAPTCHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart or in French: Fully automatic public Turing test to distinguish computers from humans.

The purpose of the tool, as the name suggests, is to detect the presence of robots by differentiating them from humans. To do this, CAPTCHA offers Internet users small questionnaires in different forms.

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What are the different types of CAPTCHAS?

CAPTCHAS provides tasks that are easily mastered by a human but which prove (in most cases) difficult for computer programs. Let’s see some examples!

Text-based CAPTCHAS

A text-based captcha code is a series of often distorted letters and numbers that must be copied by the Internet user in a given field.

It is the deformation that must make the text readable for humans but impossible for robots to interpret.

CAPTCHAS based on images

This alternative asks Internet users to recognize a given pattern and identify it on a selection of photos. In the example below, the user must click on all the images with cats above.

CAPTCHAS based on mathematical operations

These CAPTCHAS ask Internet users to do a simple mathematical calculation and to note the result in the box provided.

However, these operations also remain reasonably accessible for robots and require a second check to be more efficient.


Purchased by Google in 2009, this new verification method is based on the transcription of two words. The first of the already known and serves to identify the authenticity of the Internet user, while the second word is unknown and from a digitized book. The transcription of the same word by several Internet users allows Google to improve the scanning process and optical character recognition.

Since 2012 Google has also used reCAPTCHA to improve Google Street View by identifying street numbers on buildings.

Why use CAPTCHA on your site?

It is strongly advisable for you to install a CAPTCHA on all your site forms to protect yourself from spammers.

Free email boxes like Gmail, Hotmail, Yahoo can easily be exploited by bots that generate fake accounts in bulk and send unwanted emails. Installing CAPTCHA will help you decrease the amount of spam you receive on your work email and thus improve overall security within your company.

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Who uses a CAPTCHA?

CAPTCHAs are applied on websites that need to verify that the user is not a robot. First and foremost, CAPTCHA is used to verify online surveys. In 1999, Slashdot created a survey asking visitors to choose the postgraduate school with the best computer science program. Pupils at Carnegie Mellon and MIT universities had formed robots or automated programs to vote for their schools frequently.

These schools received thousands of votes, while others received only a few hundred. CAPTCHA has come into play so that users cannot take advantage of the voting system.

CAPTCHA is also used for registration forms on websites like Gmail or Yahoo! Mail, where people can create free accounts. CAPTCHAs deter spammers from using bots to generate a plethora of spam email accounts.

Ticket websites also use a CAPTCHA to prevent ticket resellers from buying too many tickets for high-profile events. This allows legitimate customers to buy their tickets reasonably and prevents resellers from placing thousands of orders.

Finally, web pages or blogs containing discussion forums or contact forms use CAPTCHAs to prevent spammy posts and comments. This does not put a stop to cyberbullying but blocks bots from posting messages automatically.

Fraudsters are getting smarter

Unfortunately, as technology and hackers improve, so do their scam tactics. Although CAPTCHA is generally relatively safe, cybercriminals have started embed CAPTCHAs in their bogus scam websites to make their scams more believable.

Cybercriminals can deceive internet users in several ways:

The scam contains intriguing messages on your News Feed. Ex. LEAK OF A VIDEO NEVER BROADCAST OF KIM KARDASHIAN. Once you click on this post, you will be needed to enter a fake captcha code and be taken to a landing page. At that particular point, a virus takes hold of your account.

The scam contains a strange title ex. A GIRL SENDING A TEXT DESTINED TO HER GIRLFRIEND TO HER MOTHER! Prompts users to read a story. The particular link leads to a fake news site where software piracy can begin.

How does CAPTCHA prevent the risk of fraud?

CAPTCHA offers various applications for securing websites and users.

Without being limited to this, they include:

  • Protecting email addresses
  • Protection of website registrations
  • Security of the online voting system
  • Protection against spam/email worms
  • Preventing dictionary attacks
  • Spam protection in comments on blogs.

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