Email Tracking using asp.net

try
{

    string emailTemplateBody = "Hy this is test mail";
               emailTemplateBody += "<tr><img src=''http://localhost:52583/HttpModule_using_beacon_images/images/<keyvalue>.aspx''  style=''opacity:0.0; filter:alpha(opacity=0);'' /></tr>";



    string templateName = txtTemplateName.Text;

                string toEmail = mymailaddress

    //// Get unique Key after registring mail to be sent
    string key = bl_email_calls.RegisterSystemEmailAudit("1", templateName, DateTime.Now);
    emailTemplateBody = emailTemplateBody.Replace("<keyvalue>", key);
    //// sending e-mail
    bl_email_calls.SendMailMessage(toEmail, templateName, emailTemplateBody, key);
    using (var cn = new SqlConnection(ConfigurationManager.ConnectionStrings["webConnectionString"].ToString()))
    {
       //code to insert record in database;            }
    Response.Write("Mail sent");
    // return false;
}
catch (Exception ex)
{

    throw;
}

public class HttpModuleClass : IHttpModule
    {
        //public event EventHandler BeginRequest;

        public void Dispose()
        {

        }

        /// <summary>
        /// public varibles
        /// </summary>
        string footerFile = "~/images/footer.png";
        //string footerFile = "~/images/ajax-loader.gif";
        Email_Calls bl_email_calls = new Email_Calls();

        /// <summary>
        /// Init methoed
        /// </summary>
        /// <param name="context"></param>
        public void Init(HttpApplication context)
        {
            context.BeginRequest += new System.EventHandler(GetImage_BeginRequest);
        }

        /// <summary>
        /// handles requests made to server and call update email read time
        /// </summary>
        /// <param name="sender"></param>
        /// <param name="args"></param>
        public void GetImage_BeginRequest(object sender, System.EventArgs args)
        {
            //cast the sender to a HttpApplication object
            System.Web.HttpApplication application = (System.Web.HttpApplication)sender;

            string url = application.Request.Path; //get the url path
            //string pattern = @"/HttpModule/images/(?<key>.*)\.aspx";
            //string pattern = @"/HttpModule_using_beacon_images/images/(?<key>.*)\.aspx";

            string pattern = @"/HttpModule_using_beacon_images/images/(?<key>.*)\.aspx";
            //string pattern = @"~/images/(?<key>.*)\.aspx";
            //create the regex to match for beacon images
            Regex r = new Regex(pattern, RegexOptions.Compiled | RegexOptions.IgnoreCase);
            if (r.IsMatch(url))
            {
                MatchCollection mc = r.Matches(url);
                if ((mc != null) && (mc.Count > 0))
                {
                    string key = (mc[0].Groups["key"].Value);
                    bl_email_calls.UpdateSystemEmailAuditReadDate(key);

                }

                //now send the REAL image to the client
                //application.Response.ContentType = "image/gif";
                application.Response.ContentType = "image/png";

                application.Response.WriteFile(application.Request.MapPath(footerFile));

                //end the response
                application.Response.End();
            }
        }
    }