"security" is an illusion. No matter how tight you box up your computer there's always a way to "break" it. I could disconnect my computer from the internet, and lock it up inside my room, but if I give my friend the key... well... Optical character recognition (OCR) software has been around for ages, and I know of a few people who have managed to write neural-nets to do image to text for the more garbled verifications (that even I have trouble reading with my own dam fleshy eyes! Dam you yahoo, dam you hotmail, dam you and your skwinty eyed verification systems!).
The best way to stop bots is with a series of many systems (image ver, e-mail ver, user management, a good keen eye and some brains ). That being said, many bots are either scriptkiddios or fools who are trying to sell junk, and they lack basic computer literacy, so as to be unable to "update" or alter thier bot. It's normally enough to just rename the "username" field to "realname" and the "realname" field to "username" (<input name="<username|realname>"). Hehe, I'd love to see 500 hits from a bot trying to log on with it's real name, lol. Plus, if you don't have a problem with bots yet, it's a safe bet you don't have to worry for a while
echo "deadram"; echo; fortune;