Captcha, short for “Completely Automated Public Turing test to tell Computers and Humans Apart,” is a security measure used on websites and online platforms to distinguish between human users and automated bots. It is designed to prevent bots from carrying out malicious activities such as spamming, hacking, or data scraping.

Captcha typically involves presenting users with a challenge that requires human-like intelligence to solve. This challenge can be in the form of distorted or partially obscured characters, images, puzzles, or logical questions. The purpose is to verify that the user attempting to access a website or perform a specific action is indeed a human and not a bot.

The underlying principle of Captcha is based on the fact that humans have superior ability in recognizing and interpreting visual or cognitive patterns, while bots struggle to replicate such capabilities accurately. By presenting a challenge that requires human intelligence, Captcha aims to create a barrier that only humans can overcome.

Captcha has become an integral part of various online services, including online forms, user registrations, comment sections, online polls, and e-commerce platforms. It helps protect websites from automated attacks, ensures fair access and usage of online resources, and enhances overall security and user experience.

Over time, Captcha has evolved to offer different types of challenges, such as reCAPTCHA, which combines traditional text-based challenges with image recognition tasks.