CAPTCHA Puzzle

Hey! Basically, what I need is a CAPTCHA, not words but actually a puzzle. Take a look at [login to view URL] for an example of what I want. That bots are not able to submit fake submissions is very important to my website so make sure that it's not possible to use a computer to solve it without investing huge amounts of resources. It should not require Flash as my site should work on mobile devices such as iPads, rather using Javascript. If you're able to make some type of bot to recursively download keycaptcha's collection of images to feed into this system to chop into a puzzle, that would be nice as well. Regards.