CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a security mechanism designed to distinguish human users from automated programs. It presents a challenge that is intended to be easier for people than bots to complete, such as selecting matching images, identifying visual patterns, or interacting with a checkbox. Modern CAPTCHA systems may also assess user behavior and other signals rather than relying solely on visible challenges.
CAPTCHA is commonly used on login pages, account registration forms, comment sections, and online checkout systems to reduce automated abuse, spam, credential attacks, and fraudulent submissions. Related technologies include bot detection, risk-based authentication, and rate limiting.
