A variant of IMG, called IMZ, consists of a gzipped version of a raw floppy disk image.
They also do not contain the control headers and error correction fields of CD-ROM or DVD sectors that raw disc images usually store.
Their internal format follows the structure of an optical disc file system, commonly ISO 9660 (for CDs) or UDF (for DVDs).
It was commonly used on the Atari ST line of home computers, but also with some GEM-based PC software such as Corel Ventura or Timeworks Publisher.
Garmin .img is a hard-disk image file format which contains a header and many subfiles and used to store the maps for its GPS units.