We have noticed recently that on some sites, that Google’s reCAPTCHA have included a number of numeric challenges instead of characters. We didn’t take much interest at the time but mentally noted it.
Google has today rolled out an updated version of its reCAPTCHA system. We first saw the details here. reCAPTCHA is a user-dialogue system originally developed by Luis von Ahn, Ben Maurer, Colin McMillen, David Abraham and Manuel Blum at Carnegie Mellon University's main Pittsburgh campus, and acquired by Google in September 2009. CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart”, and as its name implies, it is a quick test used in computing to determine whether or not the user is human, and one has probably seen it many times on different sites, and we even use it upon our own, however we still seem to be displaying character strings.
Generally reCAPTCHA presents two words (and the term words is used loosely): one which it knows (used to test whether you are human), and one which it doesn’t (used to help digitize the text in books). Since humans find numeric CAPTCHAs (pictured above) significantly easier to solve than those containing arbitrary text, Google will be showing you more and more numbers, which explains our observations. So we can expect to see it more often.