procedure TForm1.Button1Click(Sender: TObject);
var
ADeskTop:IActiveDesktop;
wallpaperwideChar;
begin
ADeskTop:=CreateComObject(CLSID_ActiveDesktop) as IActiveDesktop;
wallpaper:=Image1.Picture;
ADeskTop.SetWallpaper(wallpaper,0);
ADeskTop.ApplyChanges(AD_APPLY_ALL);
end;
试一试不一定行