In association with heise online

14 September 2007, 13:54

Could cats put text captchas in the doghouse?

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Captchas are used to prevent spambots from, for example, spamming blogs or opening thousands of e-mail accounts with free e-mail services and using them to send spam. However, they can often be circumvented. Microsoft's research department plans to get round these problems by getting users to distinguish between pictures of cats and dogs.

Asirra: Cat captcha interface
Microsoft is relying on more than three million images of cats and dogs, recognition of which should allow people to be distinguished from spambots.

The approach is not new - the KittenAuth project, for example, has already made use of this principle. The disadvantage in this case, however, is the small number of alternative images, which allows automated tools to learn to recognise specific images by means of characteristics such as the file hash. The Animal Species Image Recognition for Restricting Access (Asirra) research project relies on a database of more than three million images supplied by PetFinder. PetFinder presents stray animals, which are also available for adoption. The switch from captcha to catcha therefore also helps a good cause.

Asirra is currently in the beta testing phase and consists of two parts. A client-side JavaScript component is embedded in a web form on the website requiring protection. This should work in Internet Explorer 6 and 7, Firefox 2, Safari 2.0.4 and Opera 8.54 and 9.23. The second component is a web service from Microsoft, which is contacted by the server side function in order to verify whether the answer given is correct. Microsoft is currently offering the service free of charge to people interested in testing it.

See also:

  • Asirra project page from Microsoft Research


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