On a computer that is provided with a desktop kind of user interface, wallpaper is the background pattern or picture against which desktop menus, icons, and other elements are displayed and moved around. A wallpaper image can be in a JPEG or a GIF file format. Wallpaper is commonly used in Microsoft Windows, Macintosh Mac OS, Linux, and in other operating systems as well. Each operating system provides several pre-installed wallpaper images for the user to choose from. A user can also choose to download and install third-party wallpapers and use one of these instead.
Typically, a wallpaper image may be centered, stretched, or tiled. When an image is centered, it is placed in the middle of the desktop 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 or they look distorted. An image that is tiled is placed on the desktop much like tiles are placed in a shower or a tiled 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.