IMG, Disk Image File (.img)
The IMG Misc file format
IMG files are disk image files that store information otherwise available on the disk the image was created from. Such files can be stored on the hard drive of an computer but are treated by said computer like a disk drive or an optical disc. Programs like SlySoft's CloneCD can create such files as well. The IMG files received in this way hold an exact copy of a disc, thus enabling to burn an exact copy of this disc. IMG files are also created for backup reasons. In some cases, renaming an IMG file's extension from ".img" to ".iso" allows other programs to open the file.
Technical details of IMG files
Even though those IMG files were created and developed by Apple to be used on Mac OS 9 and older versions, they can also be opened on devices that run Mac OS X. By now, DMG is the new and more develop alternative to IMG files. Renaming a file with an IMG extension to display an ISO extension may, in some cases, enable other programs to view and open these files as well.