If you've ever posted a comment on a blog, signed up to a forum or submitted a URL to a search engine then you've probably encountered a CAPTCHA. One of those hard to read tests to try and prove that you're a human not an evil bot.

Sadly most of those are equally difficult for real people. The number of times I get it wrong because I can't work out if it's a "5" or an "S" or and "l" or a "1" or even read the darn thing because there's so much noise in the background picture.

Some alternatives have cropped up using types of image that a human can differentiate (men and women, cats and dogs, cheese and crackers) but most of those have a limited supply of images so it's a simple job to spend a couple of hours, map the images and break the protection.

Asirra solves the problem by accessing a large database of images that's constantly changing. Sadly the image source is puppies and kittens that are up for adoption. But as well as displaying the images to use as a security mechanism every image has an "adopt me" link underneath which links through to PetFinder to help you connect with the animal that catches your eye.

At the moment this services only features pets from the US, but it can be used to secure a page anywhere on the interweb. Hopefully in the future the service will be localized based on where the visitor is from so the pets come from a relevant source, but it's a great start.