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Generally, computers and computer programs such as bots are not capable of interpreting a CAPTCHA as they generate distorted images with text or numbers, which most Optical Character Recognition (OCR) technologies fail to make sense of. These skills enable humans to read a distorted text image or choose specific images from several different images. The concept of CAPTCHA depends on human sensory and cognitive skills. This has caused a heightened adoption of CAPTCHAs across various online businesses and services. In essence, a CAPTCHA test can tell machines/ computers and humans apart. As a type of Human Interaction Proof, or a human authentication mechanism, CAPTCHA generates challenges to identify users. Completely Automated Public Turing test, to tell Computers and Humans apart, popularly known as CAPTCHA, is a challenge-response test created to selectively restrict access to computer systems. Internet service providers generally face the risk of authentication-related attacks, spam, Denial-of-Service attacks, and data mining bots.
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