(also human verification)
CAPTCHA is a security measure used to verify that a user is not a bot (computer program) trying to access the site. The term is an acronym for “Completely Automated Public Turing test to tell Computers and Humans Apart.“ CAPTCHAs present a user with a task that a human can easily solve but that would be difficult for a computer program. For example, a person may see a distorted image of letters and numbers and then have to type the correct answer.
See also: spambot
How CAPTCHA works
- A user visits a website that requires a CAPTCHA to verify that they are human.
- The website presents the user with a challenge (e.g., a distorted image of text or a puzzle to solve).
- The user completes the challenge, verifying that they are human and not a bot.
- The website verifies the user’s response and allows them to enter the site if the answer is correct. If not, the website asks the user to try again.
- If the user fails to complete the CAPTCHA after several attempts, they may be blocked from accessing the site.
- Image-based CAPTCHA. This type of CAPTCHA shows the user an image with distorted text and asks them to correctly identify it.
- Audio-based CAPTCHA. Audio-based CAPTCHAs are used when users have difficulty seeing or interpreting image-based CAPTCHAs.
- Checkbox CAPTCHA. Checkbox CAPTCHAs ask the user to tick a box to demonstrate they are not a robot. They may also be asked some additional questions or puzzles to verify they’re human.
- reCAPTCHA. Developed by Google, reCAPTCHA uses a combination of image and text recognition. The user may be asked to identify objects in an image or transcribe distorted text.
- Game-based CAPTCHA. These CAPTCHAs require users to solve a puzzle to access the site.
- Mathematical CAPTCHA. This type of CAPTCHA gives the user a simple mathematical problem to solve.