Whilst looking into ways of protecting this blog from spam, I learnt a bit about CAPTCHA. CAPTCHA is the system of wibbly letters on coloured backgrounds that are used on many websites to help protect against spam, and does a pretty good of it too, despite being completely inaccessible. A few sites have worked around this by providing audio samples of the CAPTCHA message, although I think this is more of a fudge than a solution to spam.
I also came across a very interesting article about how the CAPTCHA system can be defeated, using neural net technology to allow the computer to 'read' the message. Whilst no code has been released, the concept looks to be quite convincing.