Google has announced a new CAPTCHA API which provides a No CAPTHA experience for most users.
For many years websites were protected with the ubiquitous CAPTCHA, but users complained about the difficulty to read some of the distorted letters. A year ago Google introduced an improved version of the visual/audio puzzle, called reCAPTCHA which is using numbers instead of letters. Users find these easier to read, and they have been useful for a while.
But the Google Maps team have developed a way to read numbers from Street View imagery using deep convolutional neural networks, presenting their finding in a scientific paper. To prove their system works, they attempted to decipher the hardest reCAPTCHA, achieving an accuracy of 99.8% in interpreting the numbers that are supposed to thwart robots.
Seeing that machine learning systems can neutralize reCAPTCHA, Google decided to use risk analysis techniques to automatically figure out if a user is human or a robot. They have improved their techniques to the point that for websites adopting the new “No CAPTCHA reCAPTCHA” most users will no longer have to solve a CAPTCHA, but simply click on a check box. If the analysis engine is not so sure that a user is human, he/she will be presented a simple test such as selecting pictures that are similar. In extreme cases, the engine falls back to the old reCAPTCHA. According to Google, early adopters of the new reCAPTCHA such as WordPress and Humble Bundle have provided a No CAPTCHA experience to 60% and respectively 80% of the users during the previous week.
The algorithms used to determine if a user is human or not are not public and most likely they will remain secret so spammers won't find ways to trick the system.
To use the new API, website developers need to acquire a key pair from Google. The new reCAPTCHA API provides a way to automatically or explicitly render the widget which is also optimized for mobile devices. The API supports users that have JavaScript disabled. Most modern browsers are supported: Chrome 3+, Firefox 3+, IE 7+, Opera 10.10+, Safari 4+.
Google provides HTML-JS and PHP examples on using the reCAPTCHA API.