How Does Captcha Code Work (In-depth Information)

How Does Captcha code works
How Does Captcha code works

You might have surely seen those random images or distorted texts asking for a solution whenever you tried accessing a particular part of a website. Well, these random-looking images & texts are non-other than the Captcha challenge. Now, for those of you who aren’t familiar with the word Captcha, let me tell you what exactly it is. A Captcha (Completely Automated Public Turing test to tell Computers and Humans apart) is a type of security guard on a website that helps a website spot the difference between a human and a bot. Moreover, it also helps in protecting a website from cyber security attacks like DDOS, and therefore, it is considered to be the most used and popular digital security system on the Internet. Although, many people around the globe are still unaware or say confused about its works. So, if you are amongst this herd, and want to know “how does Captcha code work“, then follow the article till the end. 


How does Captcha code work?

A Completely Automated Public Turing test to tell Computers and Humans apart aka Captcha, works on a simple algorithm where users are provided with Images, Text, or just a simple “I am not a robot” box, that needs to be solved or clicked as per the instructions provided.

Moreover, if seen from a reliability point of view, the Captcha bots themselves don’t know the solutions to these challenges, which makes it clear, that no matter what, bots would not be able to solve them. Not to mention, these challenges need a human brain to solve them, as they were made for humans.

Now that you have got the initial idea of how Captcha code works, we shall move to the next part, where I will be giving you subtle details of each and every Captcha challenge that is available on the internet. 

How do different types of Captcha Codes function?

To start with, let me tell you the names of some of the Captcha challenges that have been and are still used to date.

  • Classic Captcha.
  • Text-Image Captcha.
  • Audio Captcha.
  • Math Captcha.
  • Image Captcha.
  • Checkbox Captcha.
  • Invisible Captcha.

Classic Captcha:

This is the first and the oldest type of Captcha that is still used by many website users to date. Further explaining, the Classic Captcha provided website users with a Captcha challenge that had distorted text, which a user needed to type in the given box. Now, if we talk about bots, bots are a form of computers that only understand the language of zeros and ones, and therefore, they failed to solve this challenge.

Although, with the growth in Advanced Technology, the hackers were able to bypass the Classic Captcha challenge in less than 20 seconds. 

Text-Image Captcha:

After the Classic Captcha failed to protect websites from bot attacks, Google introduced its revamped version of Captcha called “reCAPTCHA” in the year 2009. reCAPTCHA service was an advanced version of Classic Captcha where users were given “Text” in the form of “Image” instead of just plain text. Moreover, Google decided to extract words and phrases from real-world objects like books, magazines, road signs, hoardings, etc.

This technology worked well for the users and was not compromised by bots until hackers got a workaround. So, what did hackers do?

Well, hackers tried solving those Text-Image Captcha codes with the help of OCR technology, which can decipher text from images and provide them with an instant solution.

Audio Captcha:

The text-image or the classic type of Captcha is an easy pass for people with healthy eyesight. But what if a person is partially or fully blind? How can he solve such Captcha challenges and continue surfing his/her favorite site?

Well, for such folks Audio Captcha was introduced, which provided the audio format of the given Captcha challenge. Thus, making it possible for a person with unhealthy eyesight to solve the Captcha code.

However, hackers were able to bypass this challenge with a shocking 99% success rate, where they managed to download the audio files of the Captcha code, and then deciphered the high-frequency sound using Google’s own Voice Recognition Software. 

Math Captcha: 

This is yet another type of Captcha code that is still used on many government websites like IRCTC and EPFINDIA. So, if we talk about it’s working, a user is given a random math problem, which he/she needs to solve to enter the webpage. 

However, it is not a foolproof solution to safeguard a website, and therefore a website holder needs to migrate to some of the best and safest options.

Image Captcha:

Image Captcha code is a type of Captcha challenge that solely depends on solving images with the help of a clue provided. For instance, a user will be given a set of 9 to 16 images and asked to pick the squares that contain a dog. So, when a user picks all those square images containing dogs and clicks on the “Verify” button, he will be automatically marked as human and allowed to pass.

However, some researchers were able to bypass the Image Captcha with a success rate of 70.78%, hence breaking the myth that Image Captcha was hard to bypass.

Checkbox Captcha:

This version of the reCaptcha challenge only demanded a visitor to click on the Checkbox that states “I am not a robot.”

Further mentioning, it examined the micro-moments of the cursor and decided whether it is a human or a bot. Plus, these micro-moments are so random that bots can’t mimic them exactly, thus making them one of the safest versions of Captcha.

However, if the Captcha bot is unable to decide whether it is a bot or a human, then it throws an Image Captcha or a Classic Captcha depending upon the score. Lower the score, the harder the challenge.

Invisible Captcha:

Finally, this is one of the latest and loved versions of reCaptcha also known as “NoCaptcha reCaptcha challenge”, where a user doesn’t need to solve any type of Captcha challenge.

In fact, it runs in the background and gives a user the score accordingly without hindering the user experience. It also uses the previously fetched cookies from the browser to determine the humanity of the user.

Why do we need Captcha Codes?

Many people wonder, why on the earth they need to implement Captcha codes on their websites, to which I can give you three solid reasons.

It protects you from harmful cyber-attacks:

A Captcha code works wonders when it comes down to preventing a website from harmful attacks like DDOS, which can harm the traffic of your website as well as ruin your reputation. 

To simply explain it, when a Captcha code is implemented on a website, a hacker won’t be able to exploit it with DDOS attacks, because a DDOS attack needs a hacker to zombify several computers which can behave like bots. Now, when it comes to bots, Captcha code works best to block them.

It prevents spam emailing:

Receiving legitimate emails helps us stay updated on our subscribed newsletters or services. But you must have also noticed that your inbox gets filled with many spammy emails. So how does this happen?

Well, a hacker or a spammer uses bots to register himself/herself with multiple email providers (non-captcha-equipped ones), thus creating multiple bogus email addresses in seconds. And therefore, as a token of protection, one should always use the Captcha code to protect against this type of abuse.

It prevents spammy comments and messages:

Lastly, if you are running a website or a blog, then you must have noticed multiple spammy comments/messages, particularly negative ones or trolls from the same user. Well, these comments/messages are posted with the help of bots, and therefore, to block them for good and save yourself from the negative limelight, Captcha codes must be used.

Who can use Captcha Code?

Anyone who is running a website whether it be a blog or business website can use Captcha code to protect their website from malicious bot attacks. 

Moreover, according to a source, in the year 1999 when Slashdot created a poll and asked the visitors to choose the best available graduate school for computer science, the students of Carnegie University and MIT created bots, which repeatedly punched votes for these two schools. Resulting in an unfair outcome.

Thus, the Captcha code can be used to protect online poll websites from such abuses.

How to protect Captcha code?

While Captcha can protect your website from random bot attacks, it is equally important to take some extra measures while implementing them, like;

Secure Images:

The images that are provided to the users must be randomly distorted because minor ones are prone to automated attacks.

Unique Captcha:

It is important to use unique Captcha codes on each and every website because a hacker can easily bypass such types of Captcha codes. Plus, one should always avoid using common mathematical equations like “2+2.”

Script Security:

Make sure that there is no easy way around the script level so that no computer can read your images. For instance, a system can pass the answer to the Captcha in plain text as a part of web form. Secondly, it is best to avoid any Captcha scripts that are found on the web, as they are more vulnerable to cyber-attacks.


Lastly, a Captcha code needs to be accessible to each and every user. Therefore, it should not only be implemented in text or image form but also in audio form.

Disadvantages of using a Captcha code.

Now that we have discussed some of the perks of using a Captcha code on a website, it is now time to look at the negative side of this digital protection tool.

Negative impact on user experience:

Now imagine this scenario, you are visiting your favorite shopping website like Ajio to shop for some fashionable attire for yourself. You picked one and then proceeded to check out, and suddenly a Captcha challenge popped up on your screen.

So, the question is, will you get annoyed?

Yes, right?

Thus, such experiences can leave a negative impact on the user experience.

It utilizes more time:

Now you might think a Captcha code takes less than 5 to 10 seconds to solve, so how can it utilize more time. Well, imagine this scenario where you have to visit 10 to 20 Captcha-equipped websites in an hour. Now, will it be feasible to solve every Captcha challenge that pop-ups in a limited frame of time? No, right? 

Thus, it can be clearly said that it utilizes more time.

May impact your conversion rates:

Now, if you are running a business website, say an eCommerce website, then placing a Captcha code on it can seriously impact your conversion rates. It is similar to the users leaving your website after getting annoyed by the poor user experience. In fact, the users may opt out of the website permanently.

Accessibility problem:

Not everyone has great eyesight to solve those text or image Captcha codes on a website, and therefore it is also essential to implement an audio challenge. But what if the audio Captcha has poor quality audio? Or what if your browser has no audio card? How will you solve it? See, that’s where the accessibility problem pops up.

Can Captcha Code be hacked?

Yes, Captcha code can be hacked or say bypassed using some of the most advanced technological methods like; automated bots, browser extensions, plugins, OCR, and captcha solving services. Moreover, as mentioned by Avanan researchers, hackers have abused reCaptcha by using a reCaptcha form sent from a legitimate domain to fool the scanners.

Can Captcha Code be a virus?

Yes, hackers can manipulate Captcha code by injecting malicious codes into the Captcha images, and then send a virus into the browser by luring the user to click on it.

Final Remarks on “How Does Captcha code work?”

Now that we have discussed, “How Captcha code works”, I hope it has given you a clear understanding of how it exactly works.

Moreover, if you are a website owner, and are planning to implement a Captcha code, then I will surely recommend you go through the preventive measures thoroughly so that the process will become easier for you.