If your images use kvm+qcow2 you can just spin up new vms as a delta image using qcow2's support for a backing store.

I want a new instance of WEBSERVER.qcow2?

    qemu-img create -b WEBSERVER.qcow2 -t qcow2 WEBSERVER-$SERIALNUMBER.qcow2 

If you're doing this as a PaaS or for CI, you do this as part of your new image creation and then pass in the new qcow2 to your vm (maybe via libvirt). If you aren't doing this or something very similar, you're spinning your wheels and wasting time/resources.