识别验证码，返回识别后的字符串，使用 tesseract 实现
    :param image_path: 图片路径
    :param broker: 券商 ['ht', 'yjb', 'gf', 'yh']
    :return recognized: verify code string

def recognize_verify_code(image_path, broker="ht"):
    """识别验证码，返回识别后的字符串，使用 tesseract 实现
    :param image_path: 图片路径
    :param broker: 券商 ['ht', 'yjb', 'gf', 'yh']
    :return recognized: verify code string"""

    if broker == "gf":
        return detect_gf_result(image_path)
    if broker in ["yh_client", "gj_client"]:
        return detect_yh_client_result(image_path)
    # 调用 tesseract 识别
    return default_verify_code_detect(image_path)