CAPTCHA Types: The 3 Bot Detectors You Need to Know (2023)

By Tibor Moes / Updated: June 2023

CAPTCHA Types: The 3 Bot Detectors You Need to Know (2023)<br />


Ever tried to crack open a walnut with your bare hands? That’s akin to a computer trying to solve a CAPTCHA. CAPTCHAs are those little puzzles you’re often asked to solve online to prove you’re human, a gatekeeper task that humans find easy but are nigh impossible for bots.


CAPTCHA, standing for Completely Automated Public Turing test to tell Computers and Humans Apart, is a type of security measure that websites use to verify that a user is human, not a bot. It’s achieved by posing tasks that are simple for humans but difficult for computers.

Type 1 – Image-based CAPTCHA: You might have encountered CAPTCHAs that ask you to identify certain images like crosswalks, cars, or traffic lights in a larger image. They’re engaging because they involve visual recognition, a task humans typically find easy but bots struggle with.

Type 2 – Math-based CAPTCHA: These CAPTCHAs require you to solve a simple math problem, like “What’s 3 + 2?”. It’s interesting because it involves logical reasoning, something humans are innately capable of, but not all bots can handle.

Type 3 – 3D CAPTCHA: One of the most advanced types of CAPTCHA, this involves rotating a 3D image or identifying an object in 3D space. It’s exciting because it involves spatial reasoning, a skill that is challenging to replicate in a bot, making it an effective barrier.

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CAPTCHA Types In-depth

Image-Based CAPTCHAs: A Visual Game of ‘Spot the Difference’

Imagine this: You’re relaxing on a Saturday afternoon, mindlessly flicking through a classic children’s book of “Spot the Difference”. As your eyes glide from one image to the next, you’re identifying slight variances—a missing hat, an extra cloud, a bird flying in the wrong direction. The human brain is incredibly adept at these visual recognition games, but did you know that this simple activity has found a crucial application on the internet? Welcome to the world of Image-based CAPTCHAs.

The term ‘CAPTCHA’, an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart, might sound like something out of a sci-fi movie. However, it’s simply a clever method that websites employ to separate human users from pesky internet bots. In the Image-based CAPTCHA variant, this is done through a visual puzzle – not unlike your ‘Spot the Difference’ game.

Here’s how it works: A user trying to access a webpage or form is presented with a selection of images, usually arranged in a grid. The images are commonplace items or scenarios—things like crosswalks, traffic lights, bicycles, buses, or fire hydrants. You, the user, are asked to select all the images that contain a specific item or scene, such as “all images with a crosswalk.”

Seems simple, right? That’s because, for a human, it is! Our brains are hardwired for this kind of pattern recognition. It’s a task that we can carry out almost without thinking.

Now, consider a computer trying to perform the same task. Computers are good at many things, but image recognition isn’t one of them—at least, not without advanced machine learning algorithms. This difference in capability between humans and machines is exactly what makes Image-based CAPTCHAs an effective tool in keeping bots at bay.

The pictures used in these CAPTCHAs often have some degree of distortion or noise to make it even harder for bots to decipher. For instance, an image might be tilted, grainy, or have elements that overlap. It’s a bit like your ‘Spot the Difference’ game got a more challenging level. This added complexity doesn’t bother humans much—we just squint a little harder, tilt our heads, and click the right boxes. But for bots? They’re left scratching their digital heads, so to speak.

So, the next time you’re online, and you come across an Image-based CAPTCHA, don’t groan in annoyance. Instead, take a moment to appreciate this clever system that’s working hard to keep your internet experience safe and secure. It’s just another day in the digital playground, and you’ve won another round of ‘Spot the Difference’ against the bots!

Math-Based CAPTCHAs: Turning Elementary Arithmetic Into a Security Shield

Picture this: you’re back in third grade, pencil in hand, working through a series of simple arithmetic problems. “What’s 5 + 3?” your teacher asks. “8!” you shout, brimming with pride. Little did you know, this elementary-level math knowledge would someday play a key role in online security, in the form of Math-based CAPTCHAs.

CAPTCHAs, or Completely Automated Public Turing tests to tell Computers and Humans Apart, are a staple in the world of internet security. They’re like an online doorman, ensuring that the user trying to access a web page or submit a form is indeed human, and not an unwanted bot. Math-based CAPTCHAs take this concept and add a numeric twist to it.

Instead of deciphering distorted text or identifying items in images, a Math-based CAPTCHA asks you to solve a simple arithmetic problem. “What’s 5 + 3?” it may ask, harking back to your third-grade classroom. You enter “8” and, voila, you’re in!

On the face of it, this might seem overly simple. After all, couldn’t a computer easily solve such straightforward math problems? Yes, in theory, a computer could solve a math problem. However, these CAPTCHAs often present the arithmetic problem as an image with varying degrees of distortion, which makes it far more difficult for bots to interpret.

Moreover, the simplicity of a Math-based CAPTCHA is part of its brilliance. It creates a barrier for bots without causing undue inconvenience to the user. Think about it: the complexity of 3D or Text-based CAPTCHAs can sometimes stump even the most tech-savvy among us. But who can’t do a bit of simple addition or subtraction?

Math-based CAPTCHAs also have the advantage of language independence. While text-based CAPTCHAs may pose difficulties for users who are not well-versed in the language used, math, as they say, is a universal language.

It’s fascinating, isn’t it, how these CAPTCHAs use our most basic human skills against sophisticated computer bots? The next time you’re asked to solve a Math-based CAPTCHA, remember: it’s not just a simple arithmetic problem. It’s a symbol of the beautiful complexities of human intelligence that we often take for granted and an ingenious shield protecting us in the digital world.

3D CAPTCHAs: A Spatial Challenge in a Flat World

Imagine you’re at a local amusement park, waiting your turn to try out the latest 3D ride. As you put on your 3D glasses and the ride starts, objects seem to pop out of the screen, and you find yourself immersed in a whole new dimension. Now, what if I told you that this same 3D technology has found a unique application in web security, through something called a 3D CAPTCHA?

CAPTCHAs, those cleverly contrived Completely Automated Public Turing tests to tell Computers and Humans Apart, serve as guardians of the internet, ensuring that a user trying to access a webpage is indeed human and not a rogue bot. The 3D CAPTCHA represents a particularly advanced version of these security tests, bringing an exciting twist to the familiar CAPTCHA formula.

3D CAPTCHAs take the principle of human superiority in image recognition, which is the cornerstone of Image-based CAPTCHAs, and push it a step further into the realm of spatial recognition. Instead of asking users to recognize or identify 2D images, 3D CAPTCHAs require users to interact with 3D models.

Here’s how it typically works: a user is presented with a 3D object or set of objects and is asked to rotate it or identify a particular aspect of it. For instance, you might be asked to rotate a 3D model of a bicycle and identify the front wheel. Easy for a human, you’d think, and you’d be right. But for a computer bot, this task presents a real headache.

You see, spatial reasoning—understanding how objects exist and interact in space—is a predominantly human skill. While we can move around a 3D world and manipulate 3D objects with ease, most bots are confined to a 2D plane. Recognizing an object from different angles, understanding the concept of ‘front’ and ‘back’—these are all surprisingly difficult tasks for a computer.

By utilizing 3D models, these CAPTCHAs are pushing the boundaries of what a computer bot can and can’t do. They effectively raise the bar in online security, ensuring that only humans can access specific web content.

So, the next time you encounter a 3D CAPTCHA, don’t see it as an annoyance. Instead, consider it an exciting ride in the amusement park of online security, a testament to our unique human capabilities, and a barrier holding the bots at bay. After all, in the world of CAPTCHAs, it’s us against the bots, and we’re winning—three dimensions at a time.


In the end, whether they’re twisting our brains with 3D models, taking us back to elementary arithmetic, or engaging us in a game of ‘Spot the Difference,’ CAPTCHAs serve as a testament to human ingenuity in the face of growing digital threats. They are our guardians in this digital era, using our uniquely human abilities to outwit the bots and keep our online experiences secure. The next time you come across a CAPTCHA, take a moment to appreciate this invisible shield, working tirelessly to keep your online world a safe space. After all, in the fascinating game of CAPTCHAs, it’s us versus the bots – and we humans are winning!

How to stay safe online:

  • Practice Strong Password Hygiene: Use a unique and complex password for each account. A password manager can help generate and store them. In addition, enable two-factor authentication (2FA) whenever available.
  • Invest in Your Safety: Buying the best antivirus for Windows 11 is key for your online security. A high-quality antivirus like Norton, McAfee, or Bitdefender will safeguard your PC from various online threats, including malware, ransomware, and spyware.
  • Be Wary of Phishing Attempts: Be cautious when receiving suspicious communications that ask for personal information. Legitimate businesses will never ask for sensitive details via email or text. Before clicking on any links, ensure the sender's authenticity.
  • Stay Informed. We cover a wide range of cybersecurity topics on our blog. And there are several credible sources offering threat reports and recommendations, such as NIST, CISA, FBI, ENISA, Symantec, Verizon, Cisco, Crowdstrike, and many more.

Happy surfing!

Frequently Asked Questions

Below are the most frequently asked questions.

What does CAPTCHA stand for?

CAPTCHA is an acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. It’s a type of online test designed to differentiate between human users and computer bots.

Why are CAPTCHAs necessary?

CAPTCHAs provide a vital security measure for websites, helping to prevent spam and automated extraction of data. By ensuring a user is human, CAPTCHAs guard against malicious activities by bots, such as mass account creation, comment spamming, or ticket purchasing for resale.

Are CAPTCHAs effective against all bots?

While CAPTCHAs are effective at thwarting many types of bots, they’re not infallible. Advanced bots using sophisticated algorithms may sometimes manage to solve CAPTCHAs. However, the continuous development of new CAPTCHA types, such as 3D CAPTCHAs, helps maintain the effectiveness of this security measure.

Author: Tibor Moes

Author: Tibor Moes

Founder & Chief Editor at SoftwareLab

Tibor is a Dutch engineer and entrepreneur. He has tested security software since 2014.

Over the years, he has tested most of the best antivirus software for Windows, Mac, Android, and iOS, as well as many VPN providers.

He uses Norton to protect his devices, CyberGhost for his privacy, and Dashlane for his passwords.

This website is hosted on a Digital Ocean server via Cloudways and is built with DIVI on WordPress.

You can find him on LinkedIn or contact him here.

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