During a process of migrating a source system into a standardized virtual environment, virtual machine instances of the source system executing in a hypervisor are snapshotted as virtual machine images in an operational repository of the hypervisor. The virtual machine images in the operational repository are short-term snapshots. From time to time during the migration process, long-term snapshots of the source system are created by checking given ones of the virtual machine images from the hypervisor operational repository into an image library as image objects.