When I store the image externally I sometimes add to the file name if I store several in a folder, but always make sure that it is named WindowsImageBackup when placing it in the external's root for discovery.
Of course if you format a primary partition on an internal drive to store it, then it is never moved and easily detectable.
But I always back it up to an external in case of HDD failure, although the only failure I've had during reimaging so far is the external crapping out.
And storing it on another network computer is a very real option once you get the hang of it. I put it in the root drive for easy detection. EDIT: YOU NEED ULTIMATE FOR THIS NETWORK STORAGE, FROM WHAT I READ TODAY.