CAPTCHA
lastmod 2025-06-12created 2022-08-115 edits
CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a type of HIP (Human Interaction Proof) technology, a method used to distinguish whether a user is a real person or a computer program. A common approach is to present an image that has been deliberately distorted or painted over so that humans can read it but computers find it hard to, and then ask what is written in the image. It is a test that transforms existing text and images into a distorted form and checks whether the subject can derive the original image from the transformed one. Images transformed by a computer program are easy for people to recognize, but computer programs cannot recognize the transformed image, so if the subject fails the test, it can be judged not to be a human. It is commonly used in places such as the anti-automated-signup programs that appear when signing up for a website.
Because CAPTCHA is a test administered by a machine to humans, it is also called a reverse Turing test (Reverse Turing test), borrowing the term from the Turing test (Turing test), which tests a machine for human-likeness.
Projects
- mCaptcha - free, open-source PoW-based CAPTCHA
- reCAPTCHA
- hCaptcha
- Cap (CAPTCHA) - lightweight, open-source PoW-based CAPTCHA alternative
- PyDoll - next-generation Python-based browser automation tool with CAPTCHA bypass features