def get_hero_image_url(hero_name, image_size="lg"):
    """
    Get a hero image based on name and image size
    """

    if hero_name.startswith("npc_dota_hero_"):
        hero_name = hero_name[len("npc_dota_hero_"):]

    valid_sizes = ['eg', 'sb', 'lg', 'full', 'vert']
    if image_size not in valid_sizes:
        raise ValueError("Not a valid hero image size")

    return "http://media.steampowered.com/apps/dota2/images/heroes/{}_{}.png".format(
        hero_name, image_size)