Microsoft Research’s Asira (Animal Species Image Recognition for Restricting Access) is a human interactive proof that provides a rather viable alternative to classical CAPTCHAs (Completely Automated Public Turing test to tell Computers and Humans Apart) that use distorted/warped texts on colourful backgrounds.
Asira is inspired by Frozen Bear’s HotCaptcha, Carnegie Mellon’s PIX CAPTCHA, Oli Warner’s KittenAuth. However, the major difference is that Asira uses a 3 million picture database from Petfinder.com while the last two have relatively small collections of images.
The inherent weakness of both KittenAuth and PIX CAPTCHA is that an attacker can easily catalog all the images available in the pool in relatively short times. While Hot CAPTCHA uses a relatively large database of images, asking users to rate whether a particular person is “hot” can be both offensive and subjective.
Asira on the other hand, partners with Petfinder.com to access its private collection of 3 million pet images. Having such a huge image database would make it computational infeasible for humans or bots to index all 3 million images available at Petfinder.com. Furthermore, only Microsoft Research has access all the images while only 10% of the 3 million images are shown on its Petfinder.com’s public website.
Though Asira is still in beta stage, you can begin using it for free. This site is already implementing Asira on its Contact Us and comments page.