IIRC they also monitor the number of requests from each IP address, and block the IP address if it exceeds the limit, I've no idea what the limits are or how long the block lasts, I'd stopped using my screen scraping software long before that was brought in.
I would of thought the CAPTCHA would be fairly easy to be overcome, you'd just need to pass the image through a decent OCR system, but the IP block would be a lot harder to overcome - you'd need to use a VPN and change the IP Once blocked, which could be pretty frequently.
Would be handy if my software still worked as I could monitor the local roll out of FTTP like I did with FTTC all those years ago.