So, how does Captcha know that I’m not a robot? This brings us to the previous question of how CAPTCHAs can still work today, even if they’re generally used less frequently than in the past.

He added: “Has anyone had that moment recently where you have failed the I-am-not-a-robot test so many times that you have that moment where you stop and go … ‘Maybe I am a robot?’ ” ...

Others felt the incident highlighted the risks of websites using the “I’m not a robot” checkbox in lieu of the more complicated CAPTCHA test.

It's getting increasingly difficult to prove you're not a robot using captcha tests, and humans are getting increasingly annoyed about it.