Google's reCaptcha technology was also based on distorted words or numbers. But they are now changing ... reCaptcha will be reduced to nothing more than a single checkbox next to the statement “I’m not a robot.” (Source here)
Instead of depending upon the traditional distorted word test, Google’s “reCaptcha” examines cues every user unwittingly provides: IP addresses and cookies provide evidence that the user is the same friendly human Google remembers from elsewhere on the Web. And Shet says even the tiny movements a user’s mouse makes as it hovers and approaches a checkbox can help reveal an automated bot.
This is a good move!