Click Start, type Power Options in the Search box, and then click Power Options on the list. In the Select a power plan window, click Change plan settings next to your selected Power plan. Click Change advanced power settings, and then expand the Desktop background settings option.

This can happen if the picture file does not match the size of your screen. For example, many home computer monitors are set at a size of 1280x1024 pixels (the number of dots that make up the image). If you use a picture file smaller than this, it will be blurry when it is stretched out to fit the screen.

To do this, right-click the image you want to set as your wallpaper, and then select Set as Desktop Background from the drop-down menu. Firefox can also position the wallpaper picture (center, tile, stretch, fill, and fit) and set the background color. You can also use a saved Internet image as a wallpaper.