A hard disk image contains an MBR, then a number of partitions, but the 'mount' instruction in Linux works with disk partitions, not full disks. To mount a partition contained in our disk image, we need to make sure the 'mount' command only sees our partition, not the whole disk.

First, lets create an empty image.

dd if=/dev/zero of=/path/to/c.img bs=516096c count=#cylinders

Now, lets set it up for mounting.

losetup /dev/loop0 /path/to/c.img

Note: Under a normal Linux setup you will need to be root to use the losetup command (The same applies to most commands we'll be using).

Now to create the MBR and partition table on the disk image (Usually you need to be root).

fdisk -u -C#cylinders -S63 -H16 /dev/loop0

Explanation:

fdisk           Linux DOS partition maintenance program.
-u              Display units in sectors not cylinders (We will need this).
-C#cylinders    Set the cylinders of disk to our value.
-S63            Set the sectors/track to 63.
-H16            Set the heads/track to 16.
/dev/loop0      Thanks to losetup this device represents our raw 'disk'.

Within fdisk use the following commands:

o - Create a new empty DOS partition table.
n - Create a new partition (For simplicity just make 1 primary partition covering the whole disk).
a - Toggle the bootable flag (Optional).
p - Print the partition table.

You should end up with a screen that looks something like this:

Disk /dev/loop0: 516 MB, 516096000 bytes
16 heads, 63 sectors/track, 1000 cylinders, total 1008000 sectors
Units = sectors of 1 * 512 = 512 bytes

      Device Boot      Start         End      Blocks   Id  System
/dev/loop0p1   *          63     1007999      503968+  83  Linux

Obviously the cylinder count, partition end and blocks will be different depending on the size of your image.

Make a note of the start sector (63 here) and the block count (503968 here).

Note: If you are intending to format the partition to something other than ext2fs then change the partition id here using the t command. I should also point out that disk manufacturers and programmers don't agree on how many bytes are in a megabyte.

w - Write partition table to our 'disk' and exit.

Ignore any errors about rereading the partition table. Since it's not a physical device we really don't care.

We now have a partition table on our disk image.

Unfortunately this also means that from here on out we have to account for the fact that our partition does not start at byte 0 of the image.