You're right in that there's no man page or info. There's an open issue
about providing such for all command line utilities. Could you help?
As you can see from the code `qvm-get-image` relies on calling in to
qubesimgconverter, and should be secure in use.
My own preference is for screenshots, but since I do this rarely, and
never for backgrounds, I am not plagued by any lack of convenience in
dealing with many files. But that is my preference.