If you have a disk image file that includes multiple partitions use the kpartx command to be able to mount each partition:

 

kpartx -v -a diskimage.img

 

This adds loop devices which you can then access from within directory /dev/mapper. Use the mount command to gain access to each partition:

 

mount -o loop /dev/mapper/loop_device /path/to/mountpoint

 

Once finished, unmount each partition mounted and then close/detach the diskimage with the command:

 

kpartx -v -d diskimage.img