Everyone knows the CAPCHA tests on websites where you either have to click on numerous pictures of cars, traffic lights, or bicycles, enter confusing combinations of numbers and letters or simply click to confirm that you’re not a robot. There used to be so many of these tests that it was downright annoying, especially if you needed several attempts.
But have you ever asked yourself whether a robot or an AI could also pass these tests? How does the CAPTCHA know that it was filled in by a human? And what does the term even stand for? Let’s clear up this mystery.
What does CAPTCHA stand for?
The word CAPTCHA stands for “completely automated public Turing Test to tell computers and humans apart” and is therefore a term for an automated, public Turing Test to distinguish humans from computers.
The term Turing Test was coined by Alan Turing, a British mathematician and computer scientist who wanted to use certain methods to test whether machines can think and act like humans. Turing tests can also be used to test AIs for creativity and awareness.
CAPTCHAs have been around since 2000 and are deliberately designed to sound similar to “capture,” as they are primarily used to intercept and filter out bots on websites, for example to avoid spam or prevent automated purchases by bots.
How does a CAPTCHA test work?
CAPTCHAs are usually quite simple, but always require you to fulfil a task. Sometimes you have to recognize certain letters and numbers that have been distorted and enter them manually. In other cases, you have to recognize certain patterns on pictures such as the existence of traffic lights, bridges, or animals.
The tests are always randomized. After reloading the website, a different task should appear each time. This is intended to avoid repetition, which would make it easier for bots to circumvent the system.
It used to be difficult for computers to solve CAPTCHAs, as certain algorithms had to be built in to reliably recognize patterns. However, the constant progress in the use of artificial intelligence has now made it possible for bots to solve these tests easily.
ninefotostudio / Shutterstock.com
ninefotostudio / Shutterstock.com
ninefotostudio / Shutterstock.com
So, how does Captcha know that I’m not a robot?
This brings us to the previous question of how CAPTCHAs can still work today, even if they’re generally used less frequently than in the past.
There’s a simple solution to this: moving the mouse. Modern CAPTCHAs use movement tracking to track the movement of the cursor. When a person moves the mouse, the route of the cursor is practically never the same. The movement is never the same speed. Bots, on the other hand, automatically click on CAPTCHA boxes or images in a perfect straight line (for example, from bottom to top directly to the box). Websites can recognize this and block access.
Occasionally, you may have to click on a box that says “I am not a robot” and then solve a more complex CAPTCHA with images again. This is because your mouse movement might’ve been more “robotic.” So next time, try a little more swerving to make it clear that you’re a human.
This article originally appeared on our sister publication PC-WELT and was translated and localized from German.
Laura is an enthusiastic gamer as well as a movie and TV fan. After studying communication science, she went straight into a job at PCMagazin and Connect Living. Since then, she has been writing about everything to do with PCs and technology topics, and has been a permanent editor at our German sister site PC-WELT since May 2024.
The letters are distorted so that bots are not likely to be able to identify them. To pass the test, users have to interpret the distorted text, type the correct letters into a form field, and submit the form. If the letters don't match, users are prompted to try again.
So, how does Captcha know that I'm not a robot? This brings us to the previous question of how CAPTCHAs can still work today, even if they're generally used less frequently than in the past. There's a simple solution to this: moving the mouse. Modern CAPTCHAs use movement tracking to track the movement of the cursor.
This information can be your cursor movement as you go to click that checkbox (apparently humans move their cursors with more randomness than a computer), your cookies and device history, according to Cloudflare. Google uses that information to determine the probability that you are a human or a robot.
A “CAPTCHA” is a turing test to tell human and bots apart. It is easy for humans to solve, but hard for “bots” and other malicious software to figure out. By adding reCAPTCHA to a site, you can block automated software while helping your welcome users to enter with ease.
Several factors can contribute to reCAPTCHA identifying you as a potential or suspected robot: Suspicious Behavior: If your interactions on the platform resemble automated or bot-like patterns, such as rapid form submissions or repeated login attempts, the system may flag them as suspicious.
If their response matches the responses from most other users who have submitted the same test, the answer is considered "correct" and the user passes the test. Picking out certain objects from blurry photos is a hard problem for computers to solve.
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A 2020 episode of QI gave a rather surprising explanation of what ticking 'I am not a robot' on a website really does. They said that it gives a website permission to look at your actions and history on your device to decide if you are human.
Google has explained it by saying that CAPTCHA can be triggered by an automated process sometimes caused by spambots, infected computers, email worms, or SEO tools. You simply need to verify it by entering the characters or clicking the correct image, and you are done.
Traditional CAPTCHAs mainly use text-based challenges, requiring users to decipher distorted or scrambled characters. On the other hand, reCAPTCHA offers a more advanced approach, incorporating image based captchas using real-world images and analyzing user behavior to distinguish between human users and bots.
Google interprets that your IP address / device sends multiple search requests at the same time (this creates a suspicious effect on the search engine). With CAPTCHA, Google makes sure that you are not a robot or a computer program that sends multiple requests for search or spam.
The takeaway. While CAPTCHAs are common, any that ask you to click “allow” are trying to trick you into subscribing to their malicious notifications. So, don't click allow if you are not a robot!
A CAPTCHA test is made up of two simple parts: a randomly generated sequence of letters and/or numbers that appear as a distorted image, and a text box. To pass a the test and prove your human identity, simply type the characters you see in the image into the text box.
Proving that you are human and not a computer programme is mainly to prevent automated software (Robots/bots) and spammers from performing actions on your behalf. CAPTCHA is a programme that is used to protect you.
One of the primary reasons bots struggle with the 'I Am Not a Robot' test lies in flawed human behavior. When a user checks the box, the system detects the action and the cursor's path. Humans tend to move the mouse more erratically and randomly in their inherent unpredictability.
Google has explained it by saying that CAPTCHA can be triggered by an automated process sometimes caused by spambots, infected computers, email worms, or SEO tools. You simply need to verify it by entering the characters or clicking the correct image, and you are done.
Robots can't pass CAPTCHA tests because they are designed to demonstrate purely human characteristics that machines cannot replicate, at least not yet. Let's not take it as a compliment, because in the first place, our lack of precision and our mistakes, are what easily distinguish us from machines.
One of the primary reasons bots struggle with the 'I Am Not a Robot' test lies in flawed human behavior. When a user checks the box, the system detects the action and the cursor's path. Humans tend to move the mouse more erratically and randomly in their inherent unpredictability.
Introduction: My name is Terrell Hackett, I am a gleaming, brainy, courageous, helpful, healthy, cooperative, graceful person who loves writing and wants to share my knowledge and understanding with you.
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