March 7, 2007 2:25 PM PST
Many Web sites use scrambled text, such as this, to ensure that a human and not a computerized bot is visiting a Web site. The trouble is that computers are getting better and better at deciphering such text. As a result, sites have been using tougher scrambles, in some cases so hard that a human can't tell either. Microsoft hopes its Asirra approach, which taps humans' ability to separate cats from dogs, will offer an easier--and cuter--option.
Photo by Carnegie Mellon University
