10.12 cannot read an APFS volume (assuming that's what was created), and to restore a volume, Casper Imaging leverages the asr command which has significant limitations when dealing with APFS (see the man page). You may not be able to continue imaging in this way unless you A) use AutoDMG to create a 10.13 HFS-formatted volume, or 2) use a 10.13 boot volume to restore the 10.13 image. No matter which direction you go, I'd look into changing how you image machines (NetInstall, or use Casper to run the macOS installer.app).
