What is a Captcha ?

A CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a type of challenge-response test used in computing to determine whether the user interacting with a website or service is a human or an automated program, like a bot.

Purpose:

CAPTCHAs are primarily used to:

  1. Prevent Spam: Block bots from posting unwanted content in forms, comments, or forums.
  2. Protect Accounts: Stop brute-force attacks on login pages by ensuring that only humans can log in.
  3. Secure Online Transactions: Prevent automated abuse during e-commerce checkout or ticket purchases.

Types of CAPTCHA:

  1. Text-based CAPTCHA: Users are asked to type distorted or obscured text from an image.
  2. Image-based CAPTCHA: Users identify specific objects in a set of images (e.g., “Select all images with traffic lights”).
  3. Audio CAPTCHA: An audio recording is played, and users must type what they hear, helping those with visual impairments.
  4. reCAPTCHA by Google:
    • reCAPTCHA v2: “I’m not a robot” checkbox, sometimes followed by an image selection challenge.
    • reCAPTCHA v3: Works in the background to assign a “human score” to user actions without requiring explicit user interaction.
  5. Behavioral CAPTCHA: Observes user behavior, like mouse movements or typing patterns, to verify humanness.
  6. Mathematical CAPTCHA: Asks users to solve a simple math problem (e.g., “What is 3 + 5?”).

How It Works:

CAPTCHAs exploit the fact that bots typically lack the advanced recognition and problem-solving abilities of humans, making them less likely to pass the test. However, advances in AI have made some CAPTCHAs less effective, leading to the development of more sophisticated systems like reCAPTCHA v3.