Remember Asirra isn’t technically a CAPTCHA. the “P” in CAPTCHA stands for public. The underlying generation algorithm and database must be publicly exposed to be a true CAPTCHA.
I don’t see how this system could work… it only has 3 million images. If I wanted to hack this system (and had millions of dollars). I would find a way to collect all 3 million pictures, then categorize them in my own database. I would outsource the categorizing to India (it could be done by a few people in a week).
Once they were categorized, I would just setup my bots with image recognition software and compare the image with my own database. Easy easy.
Snip from Microsoft Research:
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.
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 our user studies have shown that people can accomplish it quickly and accurately. Many even think it’s fun!
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