@classmethod
def splitCaptcha(cls, filepath, extension, captcha_name='captcha'):
    """ 分割验证码, 需要人工筛选放入将结果放入captcha_set目录 """
    binary_object, letters, extension = cls.captchaRecognize(filepath,
        extension, captcha_name=captcha_name)
    cls.cropImage(binary_object, letters, extension, cls.CAPTCHA_SET_PATH,
        captcha_name=captcha_name)
    if len(letters) < 4:
        raise ValueError('分割后的字符数小于4！')
