Allow only bitmapped wallpaper

Permits only bitmap images for wallpaper. This setting limits the desktop background ("wallpaper") to bitmap (.bmp) files. If users select files with other image formats, such as JPEG, GIF, PNG, or HTML, through the Browse button on the Desktop tab, the wallpaper does not load. Files that are autoconverted to a .bmp format, such as JPEG, GIF, and PNG, can be set as Wallpaper by right-clicking the image and selecting "Set as Wallpaper".

Also, see the "Desktop Wallpaper" and the "Prevent changing wallpaper" (in User Configuration\Administrative Templates\Control Panel\Display) settings.

Supported on: Windows Server 2003, Windows XP, and Windows 2000 only
Registry HiveHKEY_CURRENT_USER
Registry PathSoftware\Microsoft\Windows\CurrentVersion\Policies\ActiveDesktop
Value NameNoHTMLWallPaper
Value TypeREG_DWORD
Enabled Value1
Disabled Value0

desktop.admx

Administrative Templates (Computers)

Administrative Templates (Users)