Tuesday, July 17, 2012 9:23:58 PM
For what it's worth, I used to work in the computer graphics industry (my boss there was a member of the Joint Photographic Experts Group). As we understood it, there is no specified way for it to be pronounced, but everyone pronounced it with a hard G to prevent confusion with JIF (JPEG Interchange Format).
The "GIF Pronunciation Page" that auntiemeg32 links to points out that the Graphics File Formats FAQ states, "The pronunciation of "GIF" is specified in the GIF specification," however that is *false*. (GIF87, GIF89A)
It may have originated as "jif", but the pronunciation has drifted to "gif".