def draw_strings(draw, instrument, image_height, palette):
    """Add the strings onto the image"""
    for string_num in list(range(instrument.number_of_strings)):
        string_pos_x = (string_num * instrument.string_spacing + instrument
            .first_string_gap + instrument.margin)
        string_pos_y = instrument.top_gap + instrument.nut_width
        draw.line((string_pos_x, string_pos_y, string_pos_x, image_height),
            palette.string_colour, width=instrument.string_width)
    return draw
