/// <summary>
/// 下载验证码图片
/// </summary>
public void DownloadVerificationCodeImage()
{
string verificationCodeUrl = "https://kyfw.12306.cn/passport/captcha/captcha-image64?login_site=E&module=login";
string verificationCodeJson = HttpUtil.DoGet(verificationCodeUrl, cookieContainer);
var verificationCodeResult = JsonConvert.DeserializeObject <VerificationCodeResult>(verificationCodeJson);
FileUtil.Base64ToImageFile(verificationCodeResult.image, verificationCodePng);
ImageUtil.RgbToGrayScale(verificationCodePng, verificationCodeGrayScalePng);
}
