As you may have seen the inventor of the GIF– graphics interchange format – Steve Wilhite, has said that it should be pronounced “jif” and not “gif” (with a hard-g).
More to the point – unless you are using the animated format – you should not be using a GIF at all. Either (for photographs) use a JPEG or (for line drawings or ant graphic with 256 or less distinct colours) use a PNG.
JPEGs and PNGs, when used properly, give better quality renditions from smaller files and are essentially universally supported in browsers these days.
(If you want to know more then I recommend PNG: The Definitive Guide
Related articles
- The Creator of the GIF Says It’s Pronounced JIF. He Is Wrong (gizmodo.com)
- Creator Of The GIF Tells Us How To Pronounce It (outsidethebeltway.com)
- Father of GIFs: ‘It’s Pronounced JIF’ (mashable.com)
- An Honor for the Creator of the GIF (bits.blogs.nytimes.com)
- GIF Definition (infolific.com)
- GIF Creator Doesn’t Know How to Pronounce GIF (animalnewyork.com)
- GIF Creator, Steve Wilhite, Receives Lifetime Achievement Webby Award – NYTimes.com (bits.blogs.nytimes.com)
cartesian product 
Regardless of what Steve Wilhite says it has to be a hard ‘g’!
Unless it’s actually a Giraffics interchange format….
By the same logic, AIDS should be pronounced as the two syllable “A-ids”.