Have you ever tried to log in to an online account or submit some information to a website and Google wants to verify that you are not a robot? Probably yes!
To prove that you are human, Google reCAPTCHA usually makes you do small tasks such as check boxes that represent part of an image or just simply check a box to prove that you are not a machine. Click on a checkbox seems simple enough for a bot to do, right? So how does checking a box help to filter humans from robots?
The first reason is that there is a difference between how humans move the mouse versus how bots do it. Bots, as one would imagine, move their mouse to the exact coordinates of the box, while humans usually traverse thru the page. 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.
Secondly, how long after page load did the user find the box? Too quickly is obviously a red flag, but taking too long is also. It usually doesn’t take a legitimate human 5 minutes to answer a few questions about 9 images. If you take too long, they’ll make you do another image check challenge.
And the third known reason is that this little checkbox is basically a plugin from google, thus (via cookies, sessions, knowing your IP etc) Google knows on what pages you surfed in the time before arriving at that CAPTCHA. Knowing that you surfed for cat food or weight loss for the past 2 hours, Google can be pretty sure you’re not a robot – having to actually click on that box is basically only for “enabling” that plugin.
They are surely many tips and tricks that bots have put in use, but we do know that to beat the captcha, you’ve got a ridiculous amount of messy human behaviors to simulate which are almost unknowable.
So… that little checkbox into which we do not put much thought, is not as innocent as it seems 🙂
