def thumbstrip(arr, orientation='horizontal'):
    """Make a filmstrip from an array of images"""
    assert orientation in ['horizontal', 'vertical']
    arr_t = arr if orientation == 'vertical' else arr.swapaxes(1, 2)
    s = arr_t.shape
    arr_strip = arr_t.reshape((s[0] * s[1],) + s[2:])
    return arr_strip if orientation == 'vertical' else arr_strip.swapaxes(0, 1)
