ok listen carfully..

IMG files are like stuffed files or zipped files. very easy. The latest stuffit expander expands them all.

Then there are several other applications that make those files. Shrinkwrap, Roxio Toast and Apple's own Diskcopy are the most common.

IMG files are often used to make an exact copy of a cd.

It is NOT a graphic file.

If it's made on a mac and if you got it on a pc, then the file has no recource fork anymore and cannot be opened. To fix it read this instructions: http://www.smtips.com/dlfilespctomac.html