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What Is CAPTCHA And How Does It Work?

June 17, 2024


You’ve already established that you aren’t a robot, but websites aren’t so certain about that and may want you to confirm it. It’s nothing personal—mostly just for security measures.


This is because a lot of bots are programmed by cyber criminals to crawl the internet in search of methods to hack your sites, get access to your databases, and take your data. As a matter of fact, more than 40% of all web traffic consists of bots!


With that said, any website might fall victim to malicious bots that collect personal information, digital ad fraud, transaction fraud, and brute force assaults.


That’s why websites and browsers shield themselves against these bots through CAPTCHAs. But if you’re still kinda confused with how it all works, no worries! We’ll take you through everything you need to know about it.


Let’s get started.





“Completely Automated Public Turing Test to Tell Computers and Humans Apart” is what the abbreviation CAPTCHA stands for. That’s a mouthful to say, good thing they shortened it!


Anyways, websites utilize a challenge-response test to swiftly detect if someone is actually human or a robot. It first debuted in the late 1990s and the initial CAPTCHA tests consisted of warped graphics with a jumble of random characters and numbers. Over time, it evolved into different types (which we’ll get into later on!) which makes it harder for bots to achieve a data breach.


CAPTCHA depends on a person’s capacity and ability to spot unfamiliar patterns. Bots, on the other hand, can only do so much and can only enter random characters or follow predetermined patterns. Because of this constraint, bots are unlikely to successfully expect the right combination.


So now that you know what a CAPTCHA is, let’s get into detail on how it actually works.



How Does CAPTCHA Work?


As you’re browsing the web, you’ve probably already experienced a CAPTCHA test one way or another. You’ll be able to tell one is activated when a pop-up window will appear, asking you to pass a CAPTCHA test before you can access certain sites or enter data.


captcha test

You have to do exactly what the CAPTCHA test tells you to do. (Source: The New York Times)


A traditional text CAPTCHA will ask you to interpret distorted text and numbers in the right form field and submit the form. These twisted and bent-out-of-shape characters make it very challenging for bots to understand what is on the screen.


Alternatively, other tests might ask you to do something else like click on certain images, patterns, and the like.


So, when you’ve finally passed the CAPTCHA test, you’ll be able to enter a site or browser as normal. On the other hand, if you do end up failing it, a popup will appear again with another randomly generated CAPTCHA test and will keep repeating the process until you’re able to pass it. In some extreme cases, there are some websites that deny full access after multiple failures.



What Is CAPTCHA Used For?


captcha security

CAPTCHA is mostly used for security.


CAPTCHA is used for a lot of reasons thanks to how great it is as a security measure, especially when it comes to:


  1. Keeping an eye out for unusual transactions
    To prevent bots from acquiring limited-time products (e.g. concert tickets) and then reselling them for more in secondary markets, businesses like Ticketmaster have started implementing the CAPTCHA system.
  2. Preventing spam in product reviews and comments
    Cybercriminals and scammers can make use of any discussion forum on the internet such as blog and article comment sections to pass along scams and malware. These cybercriminals can also take part in review spam, wherein they publish several phony reviews in order to manipulate a product’s rankings on an e-commerce website or search engine. So, by requesting users to pass a CAPTCHA before publishing a comment or review, these evil deeds can be reduced.
  3. Fighting off dictionary and brute-force attacks
    Hackers can access accounts by means of brute-force and dictionary attacks, which involve bots trying every combination of letters, numbers, and special characters until they discover the right password. Luckily, these attacks can be mitigated by forcing users to complete a CAPTCHA after a specific number of failed login attempts.
  4. Avoiding false registrations
    Businesses can prevent bots from using email accounts, social media profiles, or other online services to transmit malware, spam, or engage in other illegal activities by forcing users to successfully complete a CAPTCHA test before registering for an account. Companies like Yahoo, Microsoft, and AOL were among the popular ones to use CAPTCHA because they wanted to prevent bots from opening phony email accounts.


These are just some of the usual scenarios where CAPTCHA comes in handy. Imagine if we could list down EVERY reason there is to use one. It’s pretty scary to think about, and we’re just thankful that CAPTCHA exists.



What Are The Different Types Of CAPTCHAs?


Over the years, people have been trying to fight off bots, which gave rise to different types of CAPTCHAs. Let’s quickly take a look at some of them:


1. Image-based CAPTCHAs


image-based captcha

You have to click on the image the CAPTCHA test is referring to, or the odd one out.
(Source: ResearchGate)


These CAPTCHAs make use of recognizable graphic elements, like pictures of people, things, or places. Typically, you must select photos that correspond to a subject or point out ones that do not.


Compared to other CAPTCHA types, image-based CAPTCHAs are typically simpler for people to figure out. And, since these methods demand both visual recognition and cognitive categorization, picture-based CAPTCHAs make it super challenging for bots to decipher.


With that said, for users who are blind or visually impaired, these methods bring about serious accessibility issues. That’s why this isn’t the only CAPTCHA type out there.


2. Math problem CAPTCHAs


math problem captcha

You have to solve an equation with the Math CAPTCHA. (Source: ResearchGate)


Some CAPTCHA algorithms require you to answer a straightforward math question like “4+7” or “13-10.” It is believed that a bot will have a hard time determining what question it is and coming up with an answer.


There are instances where the CAPTCHA test displays to you the characters in simple and straightforward text while some take their security to the next level by making it more confusing. They can distort and resize the numbers, add a background, and even use different colors.


3. Text-based CAPTCHAs


text-based captcha

You have to type in what characters you see with text-based CAPTCHA.
(Source: Semantic Scholar)


The most popular kind of CAPTCHAs are text-based ones, which ask users to enter a string of numbers or letters that are presented in a text box. These CAPTCHAs can make use of popular words or phrases along with random character and number combinations.


The characters are presented by the CAPTCHA in a puzzling and unclear way that demands interpretation. Characters can become confusing by being distorted, rotated, or scaled. They can also be overlaid with other visual elements like color, strokes, arcs, or spots.


Text-based CAPTCHAs can sometimes be a challenge for humans to understand what’s written, but hey, at least you know the website is safeguarded against bots with poor text recognition algorithms.


4. Audio CAPTCHAs


audio captcha

You need to type what you hear with this CAPTCHA test. (Source: Ars Technica)


Audio CAPTCHAs were developed to assist blind or visually impaired users. These CAPTCHAs are typically combined with those that use text or images and reads out a message that contains a string of characters that the user must then type in. In many cases, you can even ask for a text CAPTCHA to be converted into an MP3 audio file.


What makes these CAPTCHAs stand out is that they rely on bots’ inability to distinguish important characters from background noise. But, since there is background noise, this can sometimes make it difficult for humans to pass the CAPTCHA test.




no captcha recaptcha

You just have to click on a box to confirm you’re not a robot. (Source: WP Tavern)


This variation of CAPTCHA, made popular by Google, is a lot easier for people to figure out than the majority of others. It provides a checkbox that reads, “I am not a robot,” which users must select.


By observing user behavior, it can tell whether a click or other user action on the web page is being performed by a human or a robot. For instance, instead of only seeing that you clicked the box, Google is also keeping track of factors like your mouse movement, determining whether you moved your mouse in a predictable manner (a straight line). It will also check the cookies in your browser to see if there are any other activities that resemble human activity.


In the event that the attempt is unsuccessful, reCAPTCHA will then show a standard image selection CAPTCHA.


6. Google’s ReCAPTCHA


google recaptcha

Google raised the bar for standard CAPTCHA tests. (Source: NopeCHA)


Google offers reCAPTCHA as a free service in place of conventional CAPTCHAs. The reCAPTCHA system was developed by Carnegie Mellon University researchers and was eventually bought by Google in 2009.


When compared to standard CAPTCHA tests, reCAPTCHA is far more advanced. For instance, ReCAPTCHA gets its tests from actual imagery, such as photographs of street addresses, content from printed books, text from old newspapers, and much more.


And, just like CAPTCHA, some reCAPTCHAs require you to click on images of text that computers can’t read. This makes it so much more difficult for the usual bots to get through since they don’t have the same caliber as the reCAPTCHA tests.



What Are The Advantages Of Using CAPTCHAs?


As you may already know by now, your website can benefit in a variety of ways by adding CAPTCHA. Let’s take a look at them.


  • Website safety
    CAPTCHAs help increase the general safety of your website. By preventing harmful bot systems from submitting requests, a properly configured CAPTCHA can shield your website from malware and DDoS attacks.
  • Secured online transactions
    CAPTCHA also increases the security of online transactions, stops fraudulent website registrations or sign-ups, shields email addresses from scammers, and fights spam.
  • Improving accessibility
    While CAPTCHAs might be annoying for some users, people with impairments have a number of choices. For people who are visually handicapped, audio CAPTCHAs can be employed, and mobile-responsive designs can make it simpler for users to finish CAPTCHAs on their smartphones or other mobile devices.
  • Reducing server load
    CAPTCHAs can lessen the load on your servers by blocking bots and other programs from visiting your website. This may reduce the chance of downtime and enhance website speed.
  • Boosting SEO
    CAPTCHAs are helpful in raising your website’s search engine results by enhancing website security and lowering the threat of spam. This can help your website become more visible and attract more visitors.


The best part about all of this? Anyone can conveniently install CAPTCHA! For instance, you can easily set one up with a plugin if you’re using WordPress.



Some Limitations To CAPTCHA


As with most things, there unfortunately are also issues with CAPTCHA. Below is a list of some of them.


  • Smarter and stronger bots
    Technological advancement is great but there’s one huge problem. As technology continues to advance, so are bots. What this means is that CAPTCHA tests are becoming easier for bots to pass. For instance, advanced generative AI technology may make it simpler for bots to get around CAPTCHA verification.
  • Negative user experience
    CAPTCHA services can hinder your activity flow, causing a negative user experience on a website. Since you have to do a CAPTCHA to verify yourself every time, it can get in the way of your work schedule.
  • Not for everyone
    Not all CAPTCHAs are usable by everyone. For example, visually impaired users often struggle to solve image-based CAPTCHAs. You can’t really choose what CAPTCHA you can answer so you’re stuck with what’s offered to you.


So, no matter how great the CAPTCHA system is, you’ll find that it’s not the be-all and end-all solution to your problems.



Increase Your Web Security


As you start making your website, the most important factor that you should never overlook is security. We understand that it can get boring learning about it and trying to set everything up, but it’s one of the things that can make or break a website.


Luckily, the best web hosts are great at keeping your website safe, and these days – it’s easy to seamlessly integrate CAPTCHA to your site. With one, you can prevent bots from crawling into your website, which can result in stolen or lost data.


Having a great security system in place will grant you peace of mind knowing that all your hard work is protected from those with malicious intent!