Completely Automated Public Turing test to tell Computers and Humans Apart
A CAPTCHA is a challenge designed to be easy for humans but hard for bots, used to protect signups, logins, and forms from automated abuse. It helps blunt credential stuffing, spam, and scraping, though modern AI and cheap human solving farms have eroded its effectiveness. Many sites now use invisible behavioral analysis instead of puzzles, keeping visible challenges as a fallback.