Not gonna lie, this is a question that has kept me awake many times. But no more! Why can’t a bot tick the ‘I’m not a robot’ box?
There is difference between how humans move the mouse versus how bots do.
Google’s reCaptcha system takes advantage of the above fact to predict whether you are a human or not. Google’s reCaptcha system has a predictive model trained with sample mouse movements made by both humans and abusive bots.
As you move your mouse over the “I’m not a robot” widget towards the checkbox to click, every tiny movement is captured and sent to the predictive model.
The predictive model analyzes your mouse movements against the sample set of data and decide whether you are human or a bot.