Posted by: h4ck@lyst | October 25, 2007


Asirra is a human interactive proof that asks users to identify photos of cats and dogs. It’s powered by over three million photos from Microsoft’s unique partnership with Protect your web site with Asirra — free!

Asirra (Animal Species Image Recognition for Restricting Access) is a HIP that works by asking users to identify photographs of cats and dogs. This task difficult for computers, but user studies have shown that people can accomplish it quickly and accurately. Many even think it’s fun!

Web services are often protected with a challenge that’s supposed to be easy for people to solve, but difficult for computers. Such a challenge is often called a CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) or HIP (Human Interactive Proof). HIPs are used for many purposes, such as to reduce email and blog spam and prevent brute-force attacks on web site passwords.

HIP Example Today, the most common HIPs ask users to identify text that has been distorted or obscured, like the example seen to the right. Unfortunately, such challenges can be difficult and frustrating for people, yet are often easily solved by computers.


Protect Your Web Site with Asirra

It’s easy to add an Asirra HIP to your web site. Microsoft Research is providing it as a free web service. Be warned that Asirra is still in beta-testing; the service and its API may both be unstable.

Asirra consists of two components:

  • A JavaScript client component that you add to your web page inside a form. MS code will add an Asirra challenge to your web page. If the challenge is solved correctly, the client code gets an Asirra Ticket from MS server, and adds it to your form as a hidden input field.
  • A web service at Microsoft Research that your form processor should call each time a user form is submitted, to check that the ticket provided is valid.




  1. There is an article in about asirra- Security and Usability.

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