I never can remember those commands. So here is my memory aid.
Mount an ISO disk. It usually gets mounted in /Volumes already.
$ hdiutil mount backupdisk.iso
Mount a RAW image disk. This gets a bit more compolex – we attach the image without mounting it.
hdiutil spits out the partitions on that image and we finally mount the needed partition only.
$ hdiutil attach -imagekey diskimage-class=CRawDiskImage -nomount backupdisk.img /dev/disk5 FDisk_partition_scheme /dev/disk5s1 Windows_FAT_32 /dev/disk5s2 Linux $ mount_msdos /dev/disk5s1 ~/test
After use of the content of the image detach it with hdiutil.
$ hdiutil detach disk5 "disk5" unmounted. "disk5" ejected.