Behind the scenes. How CAPTCHA determines you're not a robot

So, how does CAPTCHA manage to differentiate between a computer and a human? The CAPTCHA system has historically been integral in distinguishing between people and automated bots. Initially, it would require typing in hard-to-read words or number strings; sometimes, it took several tries, but it was apparent how the system differentiated machines from people. Later, tasks that involved selecting photos containing specific objects, such as traffic lights, cars, hills, or animals, were introduced.

CAPTCHA often forgoes asking you to carry out any tasks, simplifying to a single question: "Are you a robot?" All you have to do is click the confirm button stating that you're not a robot, granting you access. But how does the system confirm it's not dealing with a machine? One might presume that creating an algorithm that clicks a blank field is no more difficult than identifying objects in photos. So, what's the secret behind CAPTCHA's operation?

The secret resides in that, despite only asking for a single click, CAPTCHA monitors our behavior from the moment the request appears, and sometimes even before. While creating an algorithm that clicks a button is straightforward, constructing a tool that emulates human behavior convincingly poses a far greater challenge.

"Each human movement, even the simplest one (like moving a mouse to click a button), contains an element of randomness at a microscopic level. These are minuscule, unconscious movements that algorithms can't replicate," specialists from the Cloudflare company explain on their website.

"If the cursor's movement shows this unpredictability, the test considers the user human," they elaborate. "CAPTCHA can also analyze cookies in the browser or the device's recent history."

Sandi Toksvig, the host of the QI program on this topic, adds: "For instance, if you've watched a few cat videos, liked a tweet about Greta Thunberg, and checked your Gmail account before checking the box, all these activities indicate that you're a human."

And what about the "Turing test"? The CAPTCHA definition includes a reference to it. This might seem odd, but in truth, we're dealing with a reversed Turing Test, where the machine assesses whether it's dealing with a human, not vice versa.

So next time you're asked to confirm that you're not a robot, remember that it's more than just a symbolic click. The real magic occurs much earlier.