CAPTCHA Examples: The 3 Bot Detectors to Know (2023)

By Tibor Moes / Updated: June 2023

CAPTCHA Examples: The 3 Bot Detectors to Know (2023)<br />

CAPTCHA Examples

Remember the iconic phrase ‘Are you human?’ from Sci-fi movies. Well, we’re all part of that script every time we fill out a CAPTCHA online. Acting like an astute alien hunter, CAPTCHAs sift through internet traffic to separate humans from automated ‘aliens.’ Stick around as we explore the most interesting examples.


CAPTCHAs are online test systems that differentiate between human users and automated bots. They’re typically used to prevent spam and unauthorized access, featuring tasks that are easy for humans but challenging for AI.

Example 1: Word Verification CAPTCHA (2000). Developed by AltaVista to prevent bots from adding URL to their search engine, this was the earliest CAPTCHA to gain prominence. It displayed distorted, twisted characters that humans could decipher but bots could not.

Example 2: reCAPTCHA (2007). Originated by Google, reCAPTCHA had a dual purpose – security and digitizing old books. While users transcribed words, they unknowingly helped digitize old texts that Optical Character Recognition (OCR) failed to convert.

Example 3: No CAPTCHA reCAPTCHA (2014). Evolved by Google, this CAPTCHA posed a simple question, ‘Are you a robot?’ Users checked a box to proceed, behind which a risk analysis algorithm ran, analyzing user behavior to validate human identity.

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CAPTCHA Examples In-Depth

Word Verification CAPTCHA (2000)

Imagine you’re in a bustling city, full of neon signs flashing with advertising slogans and company logos. Now, suppose someone took a few of those signs, squished them together, and then asked you to read each letter. Sound challenging? Maybe a bit, but as a human, you’re equipped with a remarkable ability to recognize patterns and decipher distorted information.

That’s exactly what the Word Verification CAPTCHA, created in the year 2000, is banking on. Pioneered by AltaVista, a popular search engine of its time, this technology was a ground-breaking weapon in the fight against pesky internet bots.

You see, back then, AltaVista was facing a rising tide of automated programs, or bots, designed to inundate their search engine with irrelevant websites. This bot-driven onslaught was leading to a poor user experience, with search results getting littered with spammy sites. Something had to be done to keep the human-friendly search results intact.

So, AltaVista’s digital knights rode into action and crafted the Word Verification CAPTCHA. This system was like an enigmatic puzzle for the bots. It displayed a series of distorted, twisted letters and numbers. While it looked like a neon-sign jumble to us, for the human brain, it was a relatively simple task to untangle the knot and identify the correct characters.

To the automated bots, however, this was an insurmountable wall. They were stumped! These bots, which were excellent at fast, repetitive tasks, couldn’t match the human brain’s ability to discern patterns and interpret visual information. They couldn’t read the twisted characters and thus were barred from adding any URLs to AltaVista’s search engine.

The Word Verification CAPTCHA, therefore, was a brilliant, and quite successful, use of humans’ inherent pattern recognition skills to ensure a smooth online experience, free from bot-induced spam.

As we navigate further into the world of CAPTCHAs, we’ll find more sophisticated versions, with each attempting to stay one step ahead in this cat-and-mouse game of internet security. However, the Word Verification CAPTCHA of 2000 will always be remembered as the pioneer that started it all!

reCAPTCHA (2007)

You’re at the kitchen table, simultaneously stirring a pot of soup and helping your child with their homework. You’re multitasking, getting two jobs done at once. This, in essence, was what Google achieved on a grand scale with its reCAPTCHA system.

The reCAPTCHA emerged as an ingenious two-birds-with-one-stone solution. While continuing the task of the traditional CAPTCHA – distinguishing humans from bots – it also took on an entirely different job – digitizing old books. Talk about efficiency!

Here’s the backstory. In 2007, Google embarked on an ambitious project to digitize the world’s books, making historical and out-of-print texts available to everyone. However, they hit a snag. Optical Character Recognition (OCR), the technology used to convert scanned books into digital text, had trouble deciphering words that were blurry, distorted, or written in old fonts. So, Google found itself with a pile of words OCR couldn’t read.

Enter reCAPTCHA. Google decided to use these hard-to-read words in their CAPTCHA tests. When you were asked to transcribe two words to prove you weren’t a bot, you were also helping Google digitize old texts. One of those words was already known to Google, serving as the test, while the other was the word OCR had trouble with.

If you and enough other people agreed on what that second word was, Google would add it to its digital library. Voila! You were simultaneously passing a security check and doing a good deed for the digital preservation of books.

It was a win-win situation, an internet version of ‘many hands make light work.’ The reCAPTCHA was not only an effective bot deterrent but also an innovative solution to a unique problem. This ingenious example of crowd-sourcing was a step forward in the world of CAPTCHA and a testament to the out-of-the-box thinking of its creators.

The next time you come across a reCAPTCHA, remember, you might just be helping to preserve a line from a centuries-old text! With this sense of shared achievement, let’s move on to explore the next advancement in the evolution of CAPTCHA technology.


Consider a wildlife photographer, camouflaged and waiting, observing an animal’s behavior to determine its species. Google’s No CAPTCHA reCAPTCHA works in a strikingly similar way, except it observes your behavior to confirm you’re a human, not a bot.

Instead of making you solve a puzzle, Google posed a seemingly simple question with this new CAPTCHA: “Are you a robot?” All you needed to do was tick a checkbox saying, “I’m not a robot.” Sounds too easy, right? You might wonder, how could such a straightforward test filter out sophisticated bots?

Well, behind the scenes of that little checkbox, Google was running an advanced risk analysis engine. It watched how you interacted with the webpage before reaching the checkbox. The speed of your mouse movements, the way you scrolled, the amount of time spent on the page, all these behavioral patterns were fed into Google’s clever engine.

You see, bots act differently than humans. Their movements are often too precise or repetitious, and they may navigate a page much faster than a human would. These behavioral differences are what Google’s system looked for.

If the system deemed your behavior human-like, you passed with a simple checkbox. But if it had doubts, you’d get a traditional CAPTCHA challenge, like transcribing distorted text or identifying objects in images.

Google’s No CAPTCHA reCAPTCHA was a significant leap forward. It made the verification process much smoother for most users while keeping the security robust. This approach embraced the idea that observing behavior could be just as effective, if not more so, than setting a challenge to separate humans from bots.

In the captivating world of CAPTCHA evolution, the No CAPTCHA reCAPTCHA marked a shift toward user-friendly and intuitive systems, balancing security and usability. As we move forward, the question is, what new ingenious CAPTCHA method will be the next to ensure our digital world remains a space for humans, not bots? Stay tuned!


In this digital age, the intriguing world of CAPTCHAs has played an essential role in keeping our online experiences human-friendly and bot-free. From the innovative Word Verification CAPTCHA in 2000 to Google’s transformative No CAPTCHA reCAPTCHA in 2014, these online bouncers have continually adapted and evolved to meet the challenges posed by ever-advancing bots. They serve as a reminder of our shared responsibility in preserving the integrity of our digital world. So, next time you encounter a CAPTCHA, take a moment to appreciate its complexity and the fascinating technology that differentiates us, humans, from the bots!

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  • 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.
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  • 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.

Why do we still need CAPTCHAs?

Despite advancements in technology, bots have become increasingly sophisticated, and the threat of spam and unauthorized access remains. CAPTCHAs serve as a line of defense, distinguishing humans from bots, and keeping online platforms secure.

Are CAPTCHAs foolproof?

While CAPTCHAs are designed to be difficult for bots to solve, they’re not foolproof. As technology evolves, so do the techniques employed by spammers and hackers. This necessitates the continuous evolution and improvement of CAPTCHA systems to keep ahead of these threats.

Why do some CAPTCHAs seem easier than others?

The difficulty of a CAPTCHA can vary based on the risk analysis performed by the system. If the system strongly believes you’re human based on your behavior, you might face a simpler challenge or even just a checkbox. However, if the system has doubts, it may present a more complex CAPTCHA to ensure security.

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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