The tutorial above is for a captcha, but it is a extremely simple one, meaning it does not provide details on auto generating graphic warps, etc. to fool ocr scanning. I like how simple the code is, but it really should have gone a step further. If you can't access the page then odds are you need to register to see it.
I beleive I am being hit by spam bots as the ip's are identical or the emails are same or my favorite localhost ip. I didn't even know they could alter the ip address. The guest book does provide banning of ip addresses and partial ip addresses, but I am banning on a daily basis and now I am not sure if those are legit ips that got banned.