Transparency
Irregularly shaped images are always contained in a rectangular box. A round button will have a rectangular background behind it. A variation of the GIF format allows you to remove the rectangular background so that only the button appears on your web page.
Background color
An easy, fast-loading way to customize your page is to define a background color in your HTML code.
Background pattern
You can use a background pattern or image, but be aware of legibility issues.
Interlaced GIFs
Because an interlaced image loads in several passes, from low resolution to high, it gives the illusion of loading faster. The viewer gets an idea of what the image looks like before it is completely loaded.
Height & width HTML tags
Always use height and width tags in your HTML. They facilitate the loading of graphics and text so that the viewer can immediately begin to read your page even before the graphics appear.
Alternate text HTML tags
Provide alternate text for your images. If the viewer has a non-graphical browser or chooses to turn off the graphics, there will still be a text description of what the graphic depicts.