You all must have at some point or the other must have come across CAPTCHA or HIP (Human Interactive Proof), which asks users to identify text that has been distorted or obscured.
HIPs are used for many purposes, such as to reduce email and blog spam and prevent brute-force attacks on web site passwords.
Unfortunately, such challenges can be difficult and frustrating for people, yet are often easily solved by computers.
Microsoft Research has developed a human interactive proof (HIP) that web sites can use to ensure their users are humans, not bots (automated scripts). 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 is difficult for computers, but people can accomplish it quickly and accurately.
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. For more info on how to add it, please refer to installation page.Also view the video on10.