$ fdisk -u -l backup-sdc6.img

Disk backup-sdc6.img: 51.0 GB, 50995924992 bytes
255 heads, 63 sectors/track, 6199 cylinders, total 99601416 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk backup-sdc6.img doesn't contain a valid partition table