The most obvious and basic image format is BMP (Bit Mapped). Each bit within a BMP file represents one pixel on the screen. Each bit fully describes the color of the pixel it represents.
As this implies, images saved in the BMP format tend to be very large. In fact, they can be huge. I've seen JPG images which are 128kb in size inflate to 1mb or more when saved as BMP.
So what is this format good for? As far as the web is concerned, there is not much use for it. I primarily use it for such things as wallpapers, logos and Desktop themes. But as far as a web sites graphics are concerned, I haven't found any use for this format.
Unless otherwise noted, all photos and text is Copyright © Richard G Lowe, Jr.