I dont no how to bacup and restore a image of firmware.
A it can be:
- they are a addon for creating a .bin or .img file of installation and save this on usb stick. About 5000 or 50.000? addons available on advanced admin menue of gl router.
- It can be, you can restore a .bin or .img file on same way like update the firmware from file by good known firmware update menue item.