I notice that almost all the answers here relate to the ineffectiveness of the concept of CAPTCHA, in principle – and while I very much agree with them, in fact gave a talk at OWASP a few months ago explaining just that – the question is very specific, so I will provide for a demonstration.
But first, I will reiterate that demonstration aside, re-read the other comments, since it’s truth that CAPTCHA is pointless and not helpful, irrelevant of implementation….
But really, check out CAPTCHA Killer. You can upload a CAPTCHA image, and it will automatically, if not immediately, provide the OCR’d answer. It also provides for an API (REST, I think, but maybe also SOAP). I personally tried numerous reCAPTCHA images, and it was actually some of the easiest ones (or at least quickest) broken.
UPDATE: CAPTCHA Killer’s website is now taken down, apparently under legal pressure. See http://captcha.org/ for a complete overview of the topic.
And yeah, OCR is not the best way to break a CAPTCHA protected site – there are many other better ways.