It has been suggested that it is difficult to capture a copy of the raspberry pi debian software.
While the actual starter SD image is pretty much whatever you get from the raspberrypi.org site(s) you might want to have your own local mirror and maintain it.
this will allow you to diverge from the main rpi raspian by replacing packages, or just have a backup for the possiblity you need a stable copy of what you are operating on, or to debug on fixed images.
Two things need to be done. one you need to get a list of mirrors for the repo(s) for raspberry pi raspbian.
here is a link to that:
here are the debian instructions for setting up a repo
More notes to follow as to how to set up the debian repo and copy a mirror.