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.
The fullform of CAPTCHA is, "Completely Automated Public Turing test to tell Computers and Humans Apart." It is a type of security test commonly used on websites in order to determine whether or not the user submitting the form comes from a computer, or a person. There are two main types of captcha systems: text-based and image-based. Image-based captcha systems are typically easier to solve than text-based because they can't be solved with traditional word methods like look up, comparison, subtraction, listing, etc.
Text based captchas work best by using words that includes numbers or letters that can be computed with word method as previously mentioned.