def _image_width(image):
    """
    Returns the width of the image found at the path supplied by `image`
    relative to your project's images directory.
    """
    if not Image:
        raise Exception("Images manipulation require PIL")
    file = StringValue(image).value
    path = None
    try:
        width = sprite_images[file][0]
    except KeyError:
        width = 0
        if callable(STATIC_ROOT):
            try:
                _file, _storage = list(STATIC_ROOT(file))[0]
                path = _storage.open(_file)
            except:
                pass
        else:
            _path = os.path.join(STATIC_ROOT, file)
            if os.path.exists(_path):
                path = open(_path, 'rb')
        if path:
            image = Image.open(path)
            size = image.size
            width = size[0]
            sprite_images[file] = size
    return NumberValue(width, 'px')