as many people have suggested to stop bots using captures with those annoying letters you can hardly read ive been on websites where you have to solve a puzzle, so what i think blizz should do is have a 4 or 6 piece puzzel to solve before entering a bg and you get 2 tries at it before you are kicked from the que
example captchas: http://www.digital-spin.com/demo.php
The Puzzle CAPTCHA
To complete this CAPTCHA the user must adjust the slider, located at the bottom left corner of the CAPTCHA, to rotate the puzzle pieces into their correctly aligned positions. This CAPTCHA is simple and elegant while remaining a very effective deterrent to bots posting spam and complete malicious registrations.It would be best suited for a blog or similar webpage, with a low to medium number of posts and traffic. This CAPTCHA can also accommodate advertisements with a link to the product or webpage of the advertiser.