reCaptcha (the one where you have to re-type a couple of random words) = yep, has been hacked some time ago.
KeyCaptcha (where you have to assemble a jigsaw puzzle of a random picture) to my knowledge hasn't been hacked yet. It's not a built in part of the human verification of VB like reCaptcha however... you have to sign up on the KeyCaptcha website to get your keys, then install the add-on. So far it seems to be working pretty well