Your best bet for that is to create a small tarball which includes a metadata.yaml file describing the image (Handling | LXD has some more details).
Once you have that, you can do lxc image import metadata.tar image.qcow2 --alias my-image which will then import it as a new local image into LXD and you can then do lxc launch my-image v1 --vm to create an instance from it.