Web page backgrounds are small images, as shown in figure below. These images blend (known as tiling) to create one large background image. You set background images up within a web editor program.
Sizes for Background Images
So why not just create a huge, single image for a background that’s tall and wide enough to cover the background of any screen size? This would eliminate the need to hide the tiling effect of backgrounds.
The answer is this:
Bigger graphics = larger file sizes = slower web pages
Large graphics will make your web pages take longer to open. A graphic that is 2 kilobytes in size takes roughly 1 second to down- load (on a 28.8 Kbps modem connection). Therefore, a graphic that’s 50 kilobytes might take around 30 seconds to download.
In web design, anything that takes more than 30 seconds to load is too large for your web page.
You also don’t want background images that are too small. Theoretically, you could create a background image the size of a single pixel. Sure, the file size of a 1-pixel graphic is small. But the problem is when web browsers tile (repeat) small graphics across and down the background of a web page, the tiling requires processing power from your computer. A smaller background image means it takes more time for your computer to tile this image.
In this tutorial: