What is a CAPTCHA? CAPTCHA Types and Examples (2024)

What is a CAPTCHA and How Do CAPTCHAs Work?

CAPTCHA, an acronym for “completely automated public Turing test to tell computers and humans apart,” isa technology used to determine whether an online user is a human or a computer program such as a bot. CAPTCHAs weredeveloped as a type of challenge-response test used in computing to distinguish between human users and automatedbots. Such tests are used to prevent automated spamming, fraud and malicious attacks on websites, as bots in generalcannot solve them with their current level of sophistication without assistance from humans.

What are CAPTCHAs Used For?

CAPTCHAs are used to protect websites and online services from spam and automated attacks by bots. By using aCAPTCHA, website owners can ensure that only humans, not bots, are accessing their website and using their services.They also prevent card and payment fraud by only allowing real users to fill out payment pages on websites andapplications.

Examples of how CAPTCHAs are used:

Securing Payment Processes
Some e-commerce websites and applications have implemented CAPTCHAs on their payment pages. This acts as anadditional step to prevent bots, which use lists of breached or stolen payment card data, from carrying outtransactions. This not only reduces payment fraud but also reduces the likelihood of the merchant being levied finesby payment processors and potentially having their merchant reputation from being harmed.

How Does a CAPTCHA Work?

A CAPTCHA works by presenting a test or puzzle that is easy for humans to solve but difficult or impossible for botsto solve. A website presents a CAPTCHA test to the user in the form of an image, audio file, or a simple questionthat requires a response. The user completes the test by providing the correct response. This response is then sentback to the website for verification using advanced algorithms to determine whether the response is likely to havebeen provided by a human or a bot. If the response is deemed to be from a bot, the user is denied access to thewebsite or service.

CAPTCHA Types and Examples

There are several different types of CAPTCHA tests that can be used to determine whether an online user is a human ora bot. The main types of CAPTCHAs are:

Text-based CAPTCHA
This type of CAPTCHA displays a series of distorted letters or numbers that the user must type into a text box. Theletters or numbers are designed to be difficult for computers to recognize but easy for humans to decipher. Examplesinclude Google's reCAPTCHA, which features distorted letters and numbers, and Cloudflare's CAPTCHA, whichincludes simple arithmetic problems.

Image-based CAPTCHA
This type of CAPTCHA displays an image that contains a specific object or shape, and the user must identify theobject or shape in the image. Image-based CAPTCHAs can be difficult for bots to recognize, as they require advancedimage recognition software. Variations of image-based CAPTCHAs offered by some providers include selecting images ofcertain objects from a collage of images, rearranging jigsaw-like images to recreate the original image, rotatingimages that the user must click on when it is upright or aligned in a certain way, and similar variations.

Audio CAPTCHA
This type of CAPTCHA is similar to image-based ones but also adds an audio recording. The user listens to a seriesof numbers, letters or words and enters them into a text box. These CAPTCHAs can be offered to users with visualimpairments or difficulty completing text-based CAPTCHAs. Many websites use an audio CAPTCHA, which features aseries of spoken letters and numbers.

Math or Word Problems
These CAPTCHAs require users to solve a simple math problem or answer a trivia question to prove that they arehuman.

Social Media Sign-in
Some websites use social media sign-in options, such as Facebook or Google, to verify that the user is a realperson. This type of CAPTCHA relies on the assumption that bots are less likely to have social media accounts.

What is the difference between reCAPTCHA and CAPTCHA?

Google’s reCAPTCHA is different from CAPTCHAs in a few ways such as the level of security and the technologyused. “CAPTCHA” is a generic term that refers to any type of challenge-response test that is used todetermine whether a user is a human or a bot. Google developed reCAPTCHA to implement advanced algorithms andmachine learning to determine whether a user is human or not, which is considered more secure than traditionalCAPTCHAs. ReCAPTCHA also includes additional security features such as IP tracking and user behavior analysis toprevent bots from getting through.

Another key difference between reCAPTCHA and CAPTCHA is the user experience. Traditional CAPTCHAs can be difficultand frustrating for users to complete. ReCAPTCHA, though, uses a range of interactive tasks, such as imagerecognition and mouse tracking, to create a more user-friendly experience. Overall, while both reCAPTCHA andtraditional CAPTCHAs serve the same basic purpose of verifying that a user is human, reCAPTCHA is considered to bemore secure and user-friendly due to its advanced technology and interactive design.

What Are the Alternatives to Using CAPTCHAs?

CAPTCHAs have long been frustrating and inconvenient for many internet users, which is why several alternatives nowprovide similar levels of security while also offering a better user experience. Common CAPTCHA alternativesare:

Honeypots
Honeypots are invisible fields that are added to web forms to detect bots. Human users can't see or interactwith these fields, but bots will try to fill them out, allowing websites to easily identify and block them.

Two-factor Authentication
Two-factor authentication (2FA) is a security process that requires users to provide two forms of identificationbefore they can access a system or service. This can include something the user knows (such as a password) andsomething they have (such as a smartphone or security token).

Behavioral Analysis
Behavioral analysis tools can be used to identify and block bots based on their browsing behavior. This mightinclude the speed at which they navigate through a website, patterns of mouse and touchpad movements or scrollingand tapping behavior on smartphones.

Email Verification
Email verification can be used to confirm the identity of a user by sending a verification link or code to theiremail address.

Social Media Log-in
Social media log-in can be used to authenticate users and confirm their identity, as many social media platformsrequire users to verify their email addresses and phone numbers.

Radware’s Crypto Challenge
Cryptochallenge mitigation is based on the cryptographic proof-of-work concept used in various blockchains anddesigned to deliver continuous, invisible browser-based challenges to suspected bots that automatically andexponentially become more difficult if solved. It uses a challenge-response model that creates a “cybercounterstrike” by forcing an attacker’s CPU to work harder and longer, thus taking a toll on theattacker’s resources. Crypto challenge also mitigates sophisticated CAPTCHA-solver and avoider bots.