Most CAPTCHA tools will use four methods of verifying that a user is human by providing a, text-based, image-based, mathematical or audio challenge.

Mathematical CAPTCHA

A mathematical challenge will be presented to a user either as part of an image or as text for them to provide the correct answer, confirming that they are a human user. It is a simple CAPTCHA to complete but also easy for bots and automated software to bypass.

Text-Based CAPTCHA

This type of CAPTCHA uses known words, phrases or random combinations of digits and letters which are presented in an image which is scaled, distorted, rotated and overlapping characters.

This provides protection against bots and algorithms which find it difficult to process text recognition and require a human user to then submit the characters before being verified as a human user.

Image-based CAPTCHA

Image-based CAPTCHA's were an improvement to CAPTCHA's which were text-based.

They require users to select images of animals, scenes or shapes which match a specific type of criteria which a human user needs to verify.

For example, selecting all of the images which contain a Cat.

 

Audio CAPTCHA

Audio CAPTCHAs were developed as an alternative that verifies a users who is visually impaired and are often used in combination with text or image-based CAPTCHAs. Audio CAPTCHAs provide an audio recording of a series of letters or numbers which a user can listen to and enter to verify.

By: Digital Chimps Support Knowledge Base, Security, Website Related: