Once the script to generate captchas is set up (see previous post) this can be easily tied into a Python web page. This assumes you are using Werkzeug and Mako, but I'm sure Django/Pylons with Jinja etc won't be too different.
In making this website and in my 4th year honours project I implemented a captcha (which you can see if you try and make a comment). I thought this would be a bit of a nightmare to do, but with Steven's help and the awesomeness of Python, it was quite easy. The code originally comes from here, but I have made a few edits such as keeping the image in memory.
30 Seconds to Mars reference management criminology Webscavator promotion Istanbul captcha chocolate piggy bank play England coasters lectures RIPA court report snob Edinburgh Fringe CV Mendeley PNG web browser forensics exhibition arts fair bibliography page breaks Snapfish statistics OCFA visualisation Brigitte Reusch Safari section breaks foodies Deterrence Theory Internet Explorer Gullane crime public lecture sock puppets art history birthday paradox demographics Sqlite Ben Nevis tea coffee Routine Activities Theory magic censorship Highland cow bacon Firefox paintings celebrities presents cases Mosaic Moroccan cuisine crime scene SECC