You can name any file
image.tar.gz, but if this .tar.gz suffix means the image is tarred and then gzipped then you're missing tar -x on the remote side. But tar -x is not designed to work in the middle of a pipeline; and it makes no sense to tar a single image of a disk in the first place. Your first command looks quite sane, but the second one (the one with image.tar.gz) does not.