What is captcha and how does it works?

We all have seen while surfing the net but do we know why does it appears and what is the purpose of that and how does it verifies that whether you are a robot or a human?This is called CAPTCHA (Complete Automated Public Turing Test to Tell Computers and Human Apart). They were invented in 2003 by researchers at Carnegie Mellon University in order to be used as a security check on a website to ensure only human’s can pass through. When you click the check box it sends over an http request with your information like your IP address your location and time the way you move your cursor before you click how you were scrolling the page time intervals and more. Most of the time the machine learning bots over Google can tell whether or not you are a robot, but if they are still unsure they will give you something like this.    And that is how Google tells that you are a human or a robot. Interesting isn’t it.