CAPTCHA is short for Completely Automated Public Turing test to tell Computers and Humans Apart. These are tests that verify whether a computing system is being operated by a human or a robot.

CAPTCHAs were built in such a way that they would need human mediation to be administered to computing systems as a part of the authentication system to ensure system security and hence prevention of unwanted looses for organizations.

Apart from summarizing how CAPTCHA works, this chapter also covers the following topics:

• Characteristics of CAPTCHAs
• Using artificial intelligence to crack CAPTCHAs
• Types of CAPTCHA
• Solving CAPTCHAs with neural networks

The following screenshot shows a CAPTCHA image that is used for verification: