How does CAPTCHA work?

How does CAPTCHA work?

• A. It uses distorted numbers or letters that no computer can recognise in order to prevent bots from joining mailing lists etc.
• B. It presents simple math problems solvable by most machines
• C. It logs user activity to verify identity
• D. It requires a biometric scan to proceed

Answer: (A)

CAPTCHA works by presenting a task that humans can perform easily but computers have a hard time finishing reliably. The classic form uses distorted characters with added background noise and variations in color and shape. A person can usually read and type these characters correctly, while automated programs struggle to recognize them due to the distortions and noise. This gap between human perception and machine recognition makes it effective at stopping bots that try to sign up for mailing lists or post spam. Other ideas don’t fit as well: simple math problems can be solved by many programs, so they’re not as robust against bots; logging user activity isn’t a test of humanity in itself but a separate tracking method; biometric scans require special hardware and raise privacy issues, making them impractical for lightweight web checks. So the distortion-based CAPTCHA approach best captures how CAPTCHAs separate humans from automated bots.

CAPTCHA works by presenting a task that humans can perform easily but computers have a hard time finishing reliably. The classic form uses distorted characters with added background noise and variations in color and shape. A person can usually read and type these characters correctly, while automated programs struggle to recognize them due to the distortions and noise. This gap between human perception and machine recognition makes it effective at stopping bots that try to sign up for mailing lists or post spam. Other ideas don’t fit as well: simple math problems can be solved by many programs, so they’re not as robust against bots; logging user activity isn’t a test of humanity in itself but a separate tracking method; biometric scans require special hardware and raise privacy issues, making them impractical for lightweight web checks. So the distortion-based CAPTCHA approach best captures how CAPTCHAs separate humans from automated bots.