The company has revealed the latest evolution of the Captcha (short, sort of, for Completely Automated Public Turing test to tell Computers and Humans Apart), which aims to do away with any interruption at all: the new, “invisible reCaptcha” aims to tell whether a given visitor is a robot or not purely by analysing their browsing behaviour. Barring a short wait while the system does its job, a typical human visitor shouldn’t have to do anything else to prove they’re not a robot.

It’s a long way from the first Captchas, introduced to stop automated programs signing up for services like email addresses and social media accounts. The idea is simple: pick a task that a human can do easily, and a machine finds very hard, and require that task be completed before the process can be continued.

The first captchas often relied on obfuscated text: a few letters and numbers, blurred, distorted, or otherwise rendered hard to parse with conventional character recognition software. Even then, they were still bypassed fairly frequently. The limited number of characters available in the Latin alphabet meant that the software could quickly improve to a passable level of accuracy, while obfuscating the letters any further could lead to real humans – particularly those with poor eyesight – being locked out.


For more references : How the internet found a better way than illegible squiggles to prove you"re not a robot 


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