CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a security measure that websites use to distinguish between human users and automated bots. You've likely encountered it when signing up for services, submitting forms, or making online purchases.

These tests typically ask you to:

• Type distorted letters and numbers from an image
• Select specific images (like traffic lights or crosswalks)
• Solve simple math problems
• Check a box labeled "I'm not a robot"

The primary purpose is preventing automated attacks including:

• Spam submissions on contact forms and comment sections
• Brute force attacks on login pages
• Ticket scalping during high-demand sales
• Fake account creation for fraudulent activities

Modern CAPTCHAs, particularly Google's reCAPTCHA, have evolved to be less intrusive. The simple checkbox version often works invisibly by analyzing your browsing behavior before showing a challenge. Only when behavior appears suspicious will it present a puzzle.

While sometimes frustrating for users, CAPTCHA serves as essential digital security infrastructure, protecting websites from abuse while allowing legitimate human traffic to proceed with minimal interruption.