How do I access a html content of an iFrame in c#?

HtmlWindow hwMain = webBrowser1.Document.Window.Frames[0];
            HtmlElementCollection eleCaptcha = hwMain.Document.GetElementsByTagName("iframe");

            foreach (HtmlElement he in eleCaptcha)
            {
                if (he.GetAttribute("name").Equals("VerifyimageFrame"))
                {
                    writeLogs(he.OuterHtml != null ? he.OuterHtml.ToString() : "Can't Find Element!");
                    he.Focus();
                    //Clipboard.SetImage(he);
                    HtmlElementCollection o = he.Document.Body.GetElementsByTagName("img");
                    foreach (HtmlElement he1 in o)
                    {
                        if (he1.GetAttribute("title").Equals("Refresh verification code"))
                        {
                            writeLogs(he1.OuterHtml != null ? he1.OuterHtml.ToString() : "Can't Find Element!");

                        }
                        else
                        {
                            MessageBox.Show("null");
                        }
                    }