Do you use the Debian from USB-stick or from the NAND? If you boot from USB-stick you can make an Image on your local linux-desktop or use a live-cd.
- put in the usb-stick into the linux-desktop
- dd if=/dev/sdb of=/path/to/image.iso
(verify the device and path)
to "reinstall"
- put in the usb-stick into the linux-desktop
- dd if=/path/to/image.iso of=/dev/sdb
(verify the device and path)
Perhaps it is also possible to only make an image of one partition. I do not tested it yet.