Microsoft's New Captcha - Cat or Not?

Microsoft came up with a new CAPTCHA idea. The CAPTCHA asks the user to classify the given photographs into a group of photos which depict a cat. This scheme is named Asirra.

The scheme is very similar to an earlier scheme called KittenAuth, in which also the CAPTCHA taker had to recognize the cat. The difference is that Microsoft is using labeled photos from www.petfinder.com and so has a huge database of images.

People who work at petfinder have done all the hard work in creating the CAPTCHA since they have labelled the photographs of the pets (cats and dogs). The claim is that the database has around 2 million images and more arrive regularly.

Humans can also adopt the pet that the like and so the creators hope that the animals will get a shelter.

Advantages of the scheme:

• Visual CAPTCHAs are always easier than the character based ones
• The test is easy to perform and is universal
• The database is very large
  

Disadvantages of the scheme:

• The scheme assumes that the database will always keep growing (what if petfinder.com stops its services?)
• Since no distortion is used, the database has to be kept a secret
• Humans are used to create the CAPTCHA (humans at petfinder.com label all the images and provide the 'difficulty' to the test. An elegant solution to this problem would not involve humans in creating it

Continuing more on the last disadvantage, does Microsoft mean that the best puzzles which the computer can NOT solve need to be human generated? Can't a computer create a puzzle which it can not solve?

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