The purpose of a CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is to protect websites from automated abuse such as spam and bot attacks. CAPTCHAs present challenges that are easy for humans to solve but difficult for automated programs, such as identifying distorted text, selecting images that meet certain criteria, or answering simple questions. By verifying that a user is human, CAPTCHAs help safeguard user accounts, secure online forms, and prevent fraudulent activity, thereby enhancing overall site security.