@classmethod
def cropImage(cls, binary_object, letters, extension, dir_path='.',
    captcha_name='captcha'):
    """ 切割二值化后的验证码图片，返回切割后的图片对象列表 """
    image_objects = []
    count = 0
    for letter in letters:
        temp_object = binary_object.crop((letter[0], 0, letter[1],
            binary_object.size[1]))
        image_path = '%s/%s.%s' % (dir_path, captcha_name +
            f'___{count + 1}', extension)
        temp_object.convert('RGB').save(image_path)
        image_objects.append(temp_object)
        count += 1
    return image_objects
