def ruokuai_captcha_handler(self, params, image_url):
        """
            若快自动识别验证码, 文档见: http://wiki.ruokuai.com/
        """

        headers = {
            'Connection': 'Keep-Alive',
            'Expect': '100-continue',
            'User-Agent': 'ben',
        }
        image_data = requests.get(image_url).content
        files = {'image': ('check_code.png', image_data)}
        r = requests.post(
            'http://api.ruokuai.com/create.json',
            data=params,
            files=files,
            headers=headers
        )
        verify_code_dict = r.json()
        if verify_code_dict:
            if 'Error' in verify_code_dict.keys():
                print (verify_code_dict['Error'])
                return ''
            verify_code = verify_code_dict.get('Result', '')
        else:
            print ('rk failed ', verify_code_dict)
            return ''

        return verify_code