The Google Blog recently posted about audio captchas — basically a way to have human authentication for people who cannot visually see web pages. Most blogs or other places using verification schemes tend to show a visually skewed image that a user must decode and enter in order to post a blog comment, signup for a web service, or things like that.

The purpose of all of these is to determine if the user is a human or a robot, mostly in an effort to thwart automatic attacks from spam bots or other nefarious robots. I think it is good to see alternative ways of verification emerging beyond the standard captcha. Though personally I don’t think they need to scramble audio, because I have a hard enough time hearing as it is!

In the bigger picture I think this points to the need for websites and web services requiring authentication to devise their own unique schemes. Part of what makes it efficient for a spammer to define measures to defeat captchas is that fact that everyone uses exactly the same one. If every blog had a slightly different way of doing it or expected response, it would raise the opportunity cost for spammers and increase their workload. While a user could easily decode sometihng like “What does 2+2=?” these types of things are not easily decoded by bots. You could also show a picture of a flower and ask someone to label it in English (or language of choice). Any of a number of options like these are quite simple tasks that a human can easily verify but a computer would have more difficutly handling. Food for thought.