Solution 1: losetup
With newer version of losetup, you can easy map parition in image file to /dev/loop*.
$ sudo losetup --show -Pf <imagefile>
/dev/loop0
The output will show which loop device has been mapped to image file. Now you can mount partition of it.
Example:
$ sudo mount /dev/loop0p1 /mnt
To detach, run sudo losetup --detach /dev/loop0.
Solution 2: qemu-nbd
Load module nbd
$ sudo modprobe nbd max_part=16
Connect /dev/nbd0 with image file
$ sudo qemu-nbd -c /dev/nbd0 <imagefile>
Update partition table
$ sudo partprobe /dev/nbd0
Mount partition of image
$ sudo mount /dev/nbd0p1 /mnt
To detach, run sudo qemu-nbd -d /dev/nbd0.