Create the page's thumbnail

def __make_thumbnail(self, width, height):
        """
        Create the page's thumbnail
        """
        (w, h) = self.size
        factor = max(
            (float(w) / width),
            (float(h) / height)
        )
        w /= factor
        h /= factor
        return self.get_image((round(w), round(h)))