FreeBSD

To mount a disk image on FreeBSD:

First attach the image to unit #1:

 # mdconfig -a -t vnode -f /big3/project/images/img/67.img -u 1

Then mount:

 # mount -t msdos /dev/md1s1 /mnt

 # ls /mnt
 BOOTLOG.PRV     BOOTLOG.TXT     COMMAND.COM     IO.SYS          MSDOS.SYS

To unmount:

 # umount /mnt
 # mdconfig -d -u 1

To mount the image read-only, use:

 # mdconfig -o readonly -a -t vnode -f /big3/project/images/img/67.img -u 1
 # mount -o ro -t msdos /dev/md1s1 /mnt

Linux

# mount -t vfat -o loop,ro,noexec img.dd /mnt

The ro is for read-only.

This will mount NSRL ISOs:

 # mount /home/simsong/RDS_218_A.iso /mnt/nsrl -t iso9660 -o loop,ro,noexec

Some raw images contains multiple partitions (e.g. full HD image). In this case, it's necessary to specify a starting offset for each partition.

# mount -t vfat -o loop,offset=32256,ro,noexec img.dd /mnt/tmp_1
# mount -t vfat -o loop,offset=20974464000,ro,noexec img.dd /mnt/tmp_2

# umount /mnt