How do you know if it’s a real human trying to sign up for an account on your website or posting a comment on your blog, or whether it’s simply a software bot leaching your resources?
The most common way today is to subject the alleged human to a CAPTCHA test, which requires he or she to type a string of letters or numbers from an obfuscated image:
Unfortunately, software bots are getting adept at solving these tests, resulting in ever increasing degrees of image obfuscation, making them difficult even for real humans to decipher.
Microsoft Research has launched a skunkworks project (codenamed “Asirra”) which comes at this from an alternative angle. Instead of forcing users to make out distorted letters, users are presented a set of 12 images of dogs and cats, and instructed to select all the cat photos. This is very easy for a human to do, but extraordinarily hard for a software bot. The images are drawn from a constantly changing database of 3 million cats and dogs, based on a partnership with Petfinder.com.
You can add Asirra for free to your website, though it’s still in beta and could be unstable. If you’re an animal lover, there is an additional reason to try this out: each animal image comes with an “Adopt Me!” link, so you can simultaneously fulfill your human authentication needs as well as find new homes for stray animals.
