CAPTCHA is a way of distinguishing humans from robots which usually come in the form of identifying various images, arithmetic problems, question-answer, riddles, simply clicking, etc. which are easily recognized, solved or answered by humans but difficult for robots. This is a preventive measure employed by companies on their websites to secure their systems are not infiltrated by suspicious hackers or attempts to steal sensitive information or any other form of cheating or security threat.
Since technology has created robots to be smarter and more human-like, there will be other creative genius who will come up with sophiscated CAPTCHAs to beat robots. Since these are products of human creations, eventually good will prevail over evil.