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CAPTCHA was invented between 1997 and 2000. It was used to protect against spam requests received every day in the now-defunct AltaVista search engine. CAPTcha offers a test that a person can easily solve, but a machine will not recognize. It helps various programs and services to identify robots and block their actions. There are many CAPTCHAs, here are the most common and frequently used CAPTchAs. The reliability of the CAPCHAs from the technical side may be questionable, but the program is undoubtedly helpful.