I will be honest with you, I personally have no clue other than the obvious. One would have to understand how each one works.
If there is a sound file available for the captcha, there would enough diktation software around to get one started.
If it is a simple picture one can get any OCR Software to try it.
If it conbsist of terrible picture … well …
Installing the tracker from my previous post will lead you sooner or later to the following website: http://deathbycaptcha.com
… and I though I had seen it all. Someone is actually making money with this. But of course you are not allowed to do anything illegal with the API … right … !!