http://www.theverge.com/2014/12/3/7325925/google-is-killing-captcha-as-we-know-it

"If you've signed up for an account recently, you've probably seen it: a quick test that gives you a few distorted words and asks you to type them back in plaintext. The official name is CAPTCHA, a test designed to weed out the automated scripts used for spam, but it's been broken for a long time. Google recently showed off a system that could crack it 99.8 percent of the time, and most spammers are happy to run their scripts knowing just one in ten will slip through. But even though everyone knows CAPTCHA is broken, there hasn't been a clear idea of what might replace it."