The CAPTCHA has been around for a while now.
We've all seen those images that pop up when you post to a blog or sign up for a free account online somewhere.
The trouble is that the spammers ability to programmatically recognize these distorted words is catching up.
The solution is to up the ante, by making the challenge harder.
How about deciding whether or not a picture contains a dog or cat?
That's what Asirra (Animal Species Image Recognition for Restricting Access) does.
Asirra is a CAPTCHA (or HIP, Human Interactive Proof) that works by asking users to identify photographs of cats and dogs.
This is a difficult task for computers, but that something people can do quickly and accurately.
Microsoft Research teamed up with Petfinder.com, the world's largest site devoted to finding homes for homeless pets.
PetFinder has a catalog of over three million images of cats and dogs, manually classified by people at thousands of animal shelters across the United States.
In exchange, Asirra provides a small "Adopt Me!" link beneath each photo, as well as wider exposure for animals needing homes.
Best of all, the site provides information on adding Asirra to your site to keep the spam bots out and help out animals in need.
Win win for everyone.