There is no more Captcha, it's now just "No CAPTCHA reCAPTCHA". Wait, is that as confusing as typing in a captcha garbled letter/number combination? Well, Google simplified it for us, just like they're trying to make protection from bots and scripts simpler but no less secure.
Instead of asking you to type out a sometimes confusing and indecipherable combination of letters and texts to prove that you're human, the No CAPTCHA reCAPTCHA lets you verify that you're not a bot just by clicking on a checkbox. You just need to fill out a few boxes the first time, but when you've proven you're not a robot, then you won't need a captcha anymore.
Mobile users, who are the ones mostly affected by the difficult garbled text you need to type out, can also get a more visual CAPTCHA challenge and all it would take is to click on the appropriate image.
While the previously difficult process was a necessary evil to protect the site from spams and bots, Google realized that Artificial Intelligence technology has become more, well, intelligent. Distorted text is now solvable, with at 99.8% accuracy (hey, that's even more accurate than most of us humans!). So they developed an Advanced Risk Analysis for reCAPTCHA that relies less on typing out distorted text but more on how a user interacts with the site. However, if the system still can't "confidently predict" that you are indeed human, then the CAPTCHA will still come out, just to be sure.
Some sites like Snapchat, WordPress, and Humble Bundle have already adapted the API and have seen an increase in traffic, or rather the users get to their sites faster due to No CAPTCHA. You can visit Google's micro-site to find out how you can adapt it to your website.
SOURCE: Google