What Is CAPTCHA?

CAPTCHA(Completely Automated Public Turing Test To Tell Computers and Humans Apart) is a system designed to differentiate between human visitors to a website and robotic agents. Administrators can validate incoming users with CAPTCHAs and websites can identify whether a user is real or malicious.

When internet users attempt to visit a website using their login credentials or enter their credit card details, they may be asked to complete a CAPTCHA. This is typically a quick step that requires them to enter a CAPTCHA code or words, click images, or complete a CAPTCHA solver to gain access to the website. 

CAPTCHA was first created as an attempt to block spam software from commenting on website pages or purchasing products in bulk. CAPTCHA forms are common on account sign-ups, online polls, and e-commerce checkouts.

The classic CAPTCHA solver asked users to identify specific letters that have been distorted so that a bot would be unlikely to recognize them. Users needed to decipher the distorted characters and type them into a form field, then submit it. If the letters were not entered correctly, the user was asked to try again.

Because spammers were able to circumvent the original CAPTCHA strategy, new strategies were developed. 2nd generation CAPTCHA required users to select images that match a certain described type. 3rd generation reCAPTCHA requires users to click on a checkbox certifying they are human (or not a robot).

The checkbox approach uses reverse logic to differentiate between robots and humans because humans drag cursors along random paths and robots move cursors in direct paths across the screen. If insufficient data is captured from the mouse movement, the 3rd generation reCAPTCHA may fall back onto a 2nd generation test.

The image test also relies on the differences between humand robot precision in selecting matching images. The image may be broken up into a grid, where humans are usually uncertain about which fragments to include. Robots tend to click in predictable patterns.

CAPTCHA enforcement has a wide range of uses that enable websites to identify real users from bots. It can be used to filter spam messages, restrict inappropriate comments, and prevent messages from posting automatically. Some websites also use CAPTCHA to protect themselves against bots and may trigger a CAPTCHA test if they detect behavior that resembles bot activity. 

CAPTCHA can prevent bots from creating multiple accounts on free services like Gmail, Hotmail, or Yahoo Mail. CAPTCHAs are placed on registration forms to prevent the creation of multiple spam email accounts.

CAPTCHAs also help websites prevent the posting of spammed messages or false comments. This is useful for blogs or web-pages that feature contact forms or message boards, ensuring only legitimate comments can be posted on them.

CAPTCHAs also help websites prevent the posting of spammed messages or false comments. This is useful for blogs or web pages that feature contact forms or message boards, ensuring only legitimate comments can be posted on them.

Websites that sell tickets to events like concerts or sports games use CAPTCHA to prevent ticket inflation and restrict the number of tickets that users can purchase. This helps them prevent scalpers from purchasing tickets in bulk then selling them for a profit or at excessive prices. This way, websites can ensure legitimate customers are able to buy tickets at fair prices.

There are several options for configuring CAPTCHA to protect websites. Common examples include:

A classic format is text-based CAPTCHA, which uses words or a combination of digits and letters that users must decipher and enter in the text box. It involves alienating or distorting letters using arcs, dots, colors, or lines to prevent bots from recognizing them.

For example, when creating a new online account, a user gets a series of distorted or contorted characters that a spambot will not be able to recognize. 

One alternative to text-based CAPTCHAs is the image-based method. Users are presented with recognizable images or graphics, such as everyday objects, and asked to select images that resemble the original image.

Other image-based CAPTCHAs ask users to select elements that are present within an image. For example, selecting all squares within an image that includes traffic lights. 

These CAPTCHA tests are quick for legitimate users to solve and more difficult for bots or computer programs to classify and solve. Therefore, image-based CAPTCHAs are a more secure alternative to text-based options.

Text and image CAPTCHAs are reliant on users being able to see the information, which restricts usage by visually impaired people. Websites can avoid this issue with audio CAPTCHAs, which typically include a button that users can select to hear an audio version of a code or sequence of letters and numbers. This increases website usability and ensures sites are available to all users. 

Another option for filtering out spam bots is to use math or word problems that users need to solve and enter the answer into the text box. These typically include simple mathematical equations or word recognition problems that users can quickly solve and enter.

Users can use their social media profile, such as a Facebook or LinkedIn account, to sign in to a service. This automatically fills in their details using a single sign-on (SSO) process.

Original CAPTCHA formats can be completed by advanced bots so they are increasingly being replaced by reCAPTCHA. The Google reCAPTCHA service provides more advanced tests that offer greater certainty between human users and bots. It sources texts and images from the real world or includes checkboxes, image recognition, and behavior assessment.

In many cases, artificial intelligence systems have a hard time identifying what would appear to be fairly simple images. For example, a "yield" sign on the road may be tough to decipher depending on the angle of the sun, shadows cast over it, or the perspective from which it's being viewed, such as nearly 90 degrees from the side. AI algorithms need massive amounts of data to be able to identify objects that may be relatively easy for humans to pick out.

So what does CAPTCHA mean for an AI computer? It’s a teaching tool. Every time human users choose the appropriate image, that data is fed back to an AI machine—helping it distinguish the differences between crosswalks and curbs, trains and trucks, stop signs and yield signs, or bicycles and motorcycles.

Fortinet FortiADC application delivery controllers enable admins to validate users through CAPTCHA. This helps businesses determine if incoming visitors are legitimate users or malicious traffic, such as bots or hackers. 

FortiADC can be configured according to the organization’s denial-of-service (DoS) and web application firewall (WAF) policy to ensure CAPTCHAs are only issued to users that meet specific rules. This provides distributed DoS (DDoS) protection, keeps applications safe from attacks through runtime application self-protection (RASP), improves website performance with a content delivery network (CDN), and enables organizations to use their own CAPTCHA verifications when attacks are detected.

CAPTCHA is an acronym for Completely Automated Public Turing Test To Tell Computers and Humans Apart. 

A classic CAPTCHA solver asks users to identify specific letters that have been distorted so that a bot would be unlikely to recognize them.

CAPTCHA enable websites to identify real users from bots. It can be used to filter spam messages, restrict inappropriate comments, and prevent messages from posting automatically.