CAPTCHA
Completely Automated Public Turing test to tell Computers and Humans Apart
A test used on websites to distinguish humans from computers and prevent automated operations by bots.
In Simple Terms
CAPTCHA is a mechanism used on websites to determine whether you're a human or an automated program. When signing up for an account, you may have seen screens asking you to type in distorted letters or select photos containing traffic lights. These challenges are used to prevent bots — automated programs — from creating accounts or flooding sites with large volumes of comments.
Behind the Name
CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart" — quite a mouthful for an acronym! It's a system designed to automatically verify that a user is human rather than an automated program. The name draws from the Turing test, a famous concept proposed by mathematician Alan Turing to determine whether a machine can exhibit intelligent behavior.
Take a Closer Look!
CAPTCHA is a technology used to tell apart humans from computers when accessing an online service.
It is commonly deployed during account registration and login to block unauthorized automated operations.
There are two main approaches to how it works.
The first is a "challenge-based format," where you solve a task — such as typing distorted characters or selecting specific images from a set. These tasks exploit human intuition and visual perception, presenting problems that are difficult for machines to solve reliably.
The second is a "behavioral analysis format," where, instead of presenting a quiz, the system silently analyzes signals like mouse movement patterns, interaction timing, device and browser information, and cookies to assess whether the user is behaving like a human.
Thanks to this technology, CAPTCHA helps curb automated abuse such as sending mass spam emails and bulk ticket purchasing by bots.
It is one of the security techniques used across the web to limit spam and block unauthorized automated activity.