How do you create your images? Do you want to have a BIG file or a SMALL file
qemu-img create debian.img 5G
this creates a large file
which is SPARSE thus is capable of being compressed
tar -cjSf debian.tar.bz2 debian.img
which can be moved.
On the other hand you can make a qcow small file to begin with.
qemu-img create debian.img -f qcow 5G
this is a small file.
And can make a copy file to use.
qemu-img create -b debian.img -f qcow stable.ovl
this second is a very tiny copy file, just stores the diffs.