An acronym for Completely Automated Public Turing test to tell Computers and Humans Apart. It's a type of security measure designed to distinguish between human users and automated computer programs (bots).
CAPTCHAs present challenges that rely on human cognitive abilities that are currently difficult for computers to replicate reliably. These challenges often involve:
Distorted Text (word captcha): Presenting text that is warped, rotated, or obscured in some way. Humans can usually decipher this text, but it's harder for OCR (Optical Character Recognition) software used by bots.
Image Recognition: Asking users to identify specific objects in a set of images (e.g., "Select all images with traffic lights"). While computers are getting better at image recognition, CAPTCHAs can still be designed to be challenging enough for bots.
Audio Challenges: Presenting audio clips of words or numbers that are distorted or have background noise. This is helpful for visually impaired users and still difficult for automated audio analysis.
Mathematical Problems: Asking users to solve simple arithmetic problems.
Logic Puzzles: Presenting simple logic or reasoning puzzles.
The most popular one is reCAPTCHA, owned by Google.
