Microsoft is working on ways to use photos of kittens, among other solutions, to help solve the spam problem.

Kevin Larson, a researcher at Microsoft's advanced reading technologies group, has found that asking a user to identify the subject of a photo, like a kitten, could help block spam programs.

Currently, services like Hotmail require new users to read and type in a string of distorted letters as proof that they're human rather than a computer. Called Human Interactive Proofs (HIPs), Microsoft and many other companies have been using the technology for around five years, Larson said at TypeCon 2007, an annual conference put on by the Society of Typographic Aficionados.

When Hotmail first started using HIPs, the number of email accounts created on the first day dropped by 20 percent without an increase in support queries, Larson said. That was a sign that the HIPs were fooling the scripts that spammers use to automate Hotmail sign-ups. However, spammers learned how to tweak their programs to better recognise the HIPs, he said.

Now, it's a race for Microsoft to continue to alter its HIP system to fool the computers, which ultimately seem to catch on. Larson's group at Microsoft experiments with different ways to distort the text used in HIPs in a way that is easy for humans to read but difficult for computers.

One twist on the HIP idea that they've worked on is to display 16 or more photos and ask for identification of the photos. In an example, he suggested using pictures of cats and dogs. The problem with the concept is that Microsoft would have to create a massive catalogue of photos, otherwise the programmers could match the correct response with each photo in the catalogue and begin to spoof the system, he said.

Audience members had a variety of ideas for ways to expand on the idea in order to try to beat the spam programs. One suggested that Microsoft continually take videos of a kitten jumping around a room, as a way to generate a nearly endless string of photos for identification.

"It's possible that kittens are the wave of the future," Larson joked.

Microsoft might also be able to use short video clips instead of photos, one audience member suggested. The cost to support that method might be a concern but it could probably work, Larson said.

His group is also working on ways to improve the current letter-based HIPs for human users. "We need to figure out how to make HIPs that are more pleasant to read," Larson said. Many computer users may be familiar with the "ugly distorted texts" that HIPs use, he said. "We let the computer science people generate this text, but this is a design problem. It seems we ought to bring what we know about legibility to make things more pleasing to identify yet still stop computers," he said.

His team has thought about using beautiful calligraphy characters set against ornate backgrounds, but such letters haven't been good at fooling the computers because a program can identify the form of the letter by the thickness of the font compared to the lines in the background design, and because a program can notice colour differences of the font compared to the background, he said.

With 90 billion pieces of spam sent every day, according to Larson, companies like Yahoo, Google and Microsoft that offer free email have an incentive to try to block spam. Otherwise they pay for the resources that help send the spam.