In a pointer from John Cox's weblog today, there's a post on the SitePoint forums that could mean the end of CAPTCHA.

From the post:

CAPTCHAs are used to filter 'flesh and blood' users from the various bots, crawlers and spiders designed to exploit web-based feedback channels. They're particularly common in areas like email and comment spam filtering systems. The idea is to set the sort of test that a human will pass easily, but bots will struggle with.

While some are still mindlessly easy -- hit reply -- others are getting so difficult that I find myself taking three or four attempts to pass. [...] So, is it just a matter of simplifying the tests? Possibly, but unfortunately the bots are fighting back. According to CAPTCHA.com, researchers at the University of California at Berkeley have developed AI software capable of 83% accuracy with Yahoo's CAPTCHA system. This will only improve.

No matter that the system that is developed, as long as there is a method behind it, it can be exploited (it seems). CAPTCHAs while good at what they're for, aren't the best for some types of input, and as mentioned in the article, can sometimes do more harm that good, driving users away from your site...