Set the wallpaper on Windows.

def set_win_wallpaper(img):
    """Set the wallpaper on Windows."""
    # There's a different command depending on the architecture
    # of Windows. We check the PROGRAMFILES envar since using
    # platform is unreliable.
    if "x86" in os.environ["PROGRAMFILES"]:
        ctypes.windll.user32.SystemParametersInfoW(20, 0, img, 3)
    else:
        ctypes.windll.user32.SystemParametersInfoA(20, 0, img, 3)