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What Is CAPTCHA? (+How to Prove You’re Human)

July 17, 2019

Our heartbeat. The blood pumping through our veins. Our brain communicating with our appendages.

These are all ways we can tell we’re human. And oftentimes, CAPTCHA makes us prove it. Sure, this effort to increase cyber security may seem annoying at times, but it helps us all in the long run. Interested in learning more? Just keep reading!


Before we can break down everything you need to know about CAPTCHA, let’s start with what it means.

CAPTCHA, which stands for Completely Automated Public Turing Test to tell Computers and Humans Apart, has become increasingly popular on a variety of websites to decrease spam and prove the legitimacy of its users.

History of CAPTCHA

Like the acronym suggests, CAPTCHA is part of the Turing Test, created by Alan Turing. Known as the father of modern computers, Turing played a large part in the history of computers, and this particular test was created as an experiment to see if machines could think or appear as humans.

During the Turing Test, an interrogator would ask two participants a series of questions. One participant is human and the other is a machine. The interrogator doesn’t know which is which and tries to guess which one is the machine. If they guess wrong, the machine has passed the Turing Test.

CAPTCHA was designed to trick machines and create a test that only a human could pass. The Turing Test was created for the CAPTCHA application to possess a variety of different types of CAPTCHA to different users, depending on their needs.

The term CAPTCHA was first officially used in 2000 by computer scientists at Carnegie Mellon University as a way to block spam software from posting comments on pages or purchasing excess items at once.

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Types of CAPTCHA

Depending on the website and the level of security it requires, it will use one of the following types of CAPTC

Text CAPTCHA: The most common type is text CAPTCHA, which requires a user to type in a series of numbers or letters displayed into a text box.


Picture recognition CAPTCHA
: Asks users to identify a set of images within a larger set of images. These are the ones we see that say “select all images with a street sign”.

Picture Recognition CAPTCHA

: This form of CAPTCHA asks a user to solve a basic math problem, like adding or subtracting two numbers together.

3D Super CAPTCHA: Requires a user to identify an image, letters, or numbers that are rendered in 3D.

Marketing CAPTCHA: Asks a user to type in a certain word or phrase that matches their brand.

I am not a robot CAPTCHA: Requires a user to check a box to specify they’re not a robot.

Audible CAPTCHA: Presents the user with a series of spoken letters or numbers. Often a user can request a text CAPTCHA be rendered as an MP3 audio file.

Did you know? Humans have about an 80% success rate at solving CAPTCHA, while machines have a success rate of 0.1%, according to Microsoft.

Most of these types of CAPTCHAs are visual tests. This is because computers aren’t advanced enough (yet) to process visual data the way humans can. Even so, it’s important to keep accessibility in mind if you’re a website interested in taking advantage of CAPTCHA. Having an alternative to a visual CAPTCHA, like audible CAPTCHA, is a must for visually-impaired users.

How CAPTCHA keeps websites secure

The reason so many websites are using CAPTCHA is because of the increase in spam. The types of CAPTCHA provide ways for these websites to check if a person registering, making a purchase, or commenting is a real human, as opposed to a computer program or machine looking to flood the site with spam.

While we as users often find entering text or clicking on a series of photos annoying and time-consuming, it’s worth it in the long run. Imagine trying to buy concert tickets to see your favorite band, only for spam bots to swoop in and purchase 100 of them at once. Thanks to CAPTCHA, we can be sure that only real humans are buying these tickets.

If a website or blog owner doesn't implore CAPTCHA, they would receive dozens of spam comments, purchases, and traffic sessions a day. In addition, CAPTCHA also protects email addresses from scammers, website registrations, online polling, and junk mail.

Related: If you’re a website owner and are unsure about what bot detection and mitigation software is and which one would be best for your business, check out this comprehensive list, brought to you by G2!

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Google’s reCAPTCHA

reCAPTCHA was bought by Google in 2009. This software works to guess whether a session is initiated by a human or a bot based on the behavior when the page is loading.

If it isn’t able to tell if there’s a human or a bot behind the session, it will distribute one of two tests. The first being the “click here to prove you’re human” box or a visual puzzle based on Google Images photos.

According to Google, “reCAPTCHA is a free service that protects your website from spam and abuse. reCAPTCHA uses an advanced risk analysis engine and adaptive challenges to keep automated software from engaging in abusive activities on your site. It does this while letting your valid users pass through with ease.”

They list the advantages to their reCAPTCHA software as providing advanced security, being easy to use, and creating value, all while using deep learning and machine learning to do so. Google states, “Hundreds of millions of CAPTCHAs are solved by people every day. reCAPTCHA makes positive use of this human effort by channeling the time spent solving CAPTCHAs into digitizing text, annotating images, building machine learning datasets. This helps preserve books, improve maps, and solve hard AI problems.”

You’ll find that Google uses its reCAPTCHA software when you:

  • Sign up for a new Google service, like Gmail or YouTube
  • Sign up for any edition of a G Suite account
  • Change a password on an existing account
  • Setup Google services for a third-party device, like an iPhone

Be a good human

Or at least, be good at proving you’re a human to CAPTCHA. It’s the only way you’ll be able to buy those last-minute concert tickets or post an encouraging comment on a blog.

Learn more about digital security threats, like phishing and spyware, so you can better protect your personal information.

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