Google ReCaptcha Answer RRS feed

  • Question

  • Hello,

    I have that code for creating a recaptcha image from google:

    public Image CreateRecaptcha(string key, ref string challenge)
                    WebClient client = new WebClient();
                    string response = client.DownloadString(string.Format("{0}", key));
                    Match match = Regex.Match(response, "challenge : '(.+?)'");
                    if (match.Captures.Count == 0)
                        challenge = null;
                        return null;
                    challenge = match.Groups[1].Value;
                    if (File.Exists("captcha.jpg")) File.Delete("captcha.jpg");
                    client.DownloadFile(string.Format("{0}", challenge),
                    return Image.FromFile("captcha.jpg");
                catch (Exception)
                    challenge = null;
                    return null;
    It is working fine and I get the image.
    The only thing I need is to get the string with the answer for the image (the text that appears on it).
    Can someone help me getting the answer from that method?
    I believe it's related to the 'challenge' and 'key' but I just couldn't find what to do with it.
    Friday, March 9, 2018 10:41 AM

All replies

  • Although the following is for ASP.NET you can still learn from it.

    using Newtonsoft.Json;
    public class ReCaptchaClass
        public static string Validate(string EncodedResponse)
            var client = new System.Net.WebClient();
            string PrivateKey = "6LcH-v8SerfgAPlLLffghrITSL9xM7XLrz8aeory";
            var GoogleReply = client.DownloadString(string.Format("{0}&response={1}", PrivateKey, EncodedResponse));
            var captchaResponse = Newtonsoft.Json.JsonConvert.DeserializeObject<ReCaptchaClass>(GoogleReply);
            return captchaResponse.Success;
        public string Success
            get { return m_Success; }
            set { m_Success = value; }
        private string m_Success;
        public List<string> ErrorCodes
            get { return m_ErrorCodes; }
            set { m_ErrorCodes = value; }
        private List<string> m_ErrorCodes;

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    Friday, March 9, 2018 12:30 PM