On desktop computers, wallpaper is the background pattern or picture against which the menus, icons, activewindows, and other elements are displayed and moved around on the screen. A wallpaper image can be in a JPG or a GIF file format. Wallpaper is commonly used in Microsoft Windows, Macintosh OS, Linux, and in other operating systems as well. Each operating system provides several "pre-installed" wallpaper images for users to choose from. You can also choose to download and install "third-party" wallpapers or use an image of your own instead.
Typically, a wallpaper image may be centered, stretched, or tiled. When an image is centered, it is placed in the middle of the screen and is surrounded by a solid color. When an image is stretched, it is stretched to cover all of the desktop. Only certain images can be stretched otherwise they look distorted. An image that is tiled is placed on the desktop and repeated several times, much like tiles are placed on a floor. "Tiling" is commonly used for patterns instead of photos because a pattern is one square image that repeats itself across and down the screen, effectively forming a single image.