<asp:UpdatePanel runat="server" ID="upleft" UpdateMode="Conditional" >
      <ContentTemplate>
    <asp:DataList ID="DataListLeft" runat="server" 
        BackColor="LightGoldenrodYellow" 
        BorderColor="Tan" BorderWidth="1px" CellPadding="2" 
        DataSourceID="SqlDataSource1" Width="524px" ForeColor="Black">
        <FooterStyle BackColor="Tan" />
        <AlternatingItemStyle BackColor="PaleGoldenrod" />
        <SelectedItemStyle BackColor="DarkSlateBlue" ForeColor="GhostWhite" />
        <HeaderStyle BackColor="Tan" Font-Bold="True" />
        <ItemTemplate>
            <table>
                <tr>
                    <td>Nick Name
                    </td>
                    <td>Content
                    </td>
                </tr>
                <tr>
                    <td><asp:Label ID="ST_r_nickLabel" runat="server" 
                          Text='<%# Eval("ST_r_nick") %>' />
                    </td>
                    <td><asp:Label ID="ST_r_contentLabel" runat="server" 
                          Text='<%# Eval("ST_r_content") %>' />
                    </td>
                </tr>
            </table>
        </ItemTemplate>
         <SeparatorTemplate>
            <img alt="" src="images/Hr_book_pen.gif" />
        </SeparatorTemplate>
    </asp:DataList>
    <br />
    <asp:Label ID="lblMessage" runat="server" ForeColor="Red"></asp:Label>
    </ContentTemplate>
    <Triggers>
        <asp:AsyncPostBackTrigger ControlID="replay" EventName="Click" />
    </Triggers>
    </asp:UpdatePanel>
    <asp:SqlDataSource ID="SqlDataSource1" runat="server" 
        ConnectionString="<%$ ConnectionStrings:ConnectionString %>" 
        SelectCommand=
"SELECT [ST_r_nick], [ST_r_content] FROM [ST_replay] Where ST_n_id=@ST_n_id"
        >
    <SelectParameters>
        <asp:QueryStringParameter  Name="ST_n_id" QueryStringField="id" 
          Type="Int32"/>
    </SelectParameters>
</asp:SqlDataSource>

// render the verfication code
public void ProcessRequest (HttpContext context) 
{
    // Create the Bitmap
    using (Bitmap objBitmap = new Bitmap(_width, _height, 
      PixelFormat.Format32bppArgb))
    {
        // create the canvas
        using (Graphics objGraphics = Graphics.FromImage(objBitmap))
        {
            //specify the smoothing mode 
            objGraphics.SmoothingMode = SmoothingMode.AntiAlias;
 
            //Define a rectangle to render the verfication code
            Rectangle rect = new Rectangle(0, 0, _width, _height);
            
            //define a brush with specified hatching style
            HatchBrush hBr = new HatchBrush(HatchStyle.WideDownwardDiagonal, 
                                              Color.Yellow, Color.White);
            // create a rectangle for renderiing picture
            objGraphics.FillRectangle(hBr, rect);
            hBr.Dispose();
            
            // define the character offset in the string
            int charOffset = 0;
            //compute the width for each character
            double charWidth = 
              Convert.ToDouble(_width) / Convert.ToDouble(_randomTextLength);
            //look on per character as a rectangle so as to twist it easily
            Rectangle rectChar;
            // define the  fond style
            Font fnt = null;
            
            //first use a black color brush to render the 
            //letter within the rectangle, then twist the 
            //rectangle, and at last use the rectangle to draw
            using (Brush br = new SolidBrush(Color.Black))
            {
                foreach (Char ch in _randomText)
                {
                    fnt = GetFontStyle();
                    rectChar = new Rectangle(Convert.ToInt32(charOffset * charWidth), 
                      0, Convert.ToInt32(charWidth), _height);
 
                    GraphicsPath gp = TextPath(ch.ToString(), fnt, rectChar);
                    TwistText(gp, rectChar);
                    objGraphics.FillPath(br, gp);
                    charOffset += 1;
                }
            }
 
            // add some background noise points as well as the line noise
            AddNoise(objGraphics, rect);
            AddLine(objGraphics, rect);
 
            // specify the ContentType of the Response object
            //, and require when the drawing is finished 
            // return the result to the browser side                
            context.Response.ContentType = "Image/Jpeg";
            context.Response.Clear();
            // set the Cache-Control: no-cache
            context.Response.Cache.SetCacheability(HttpCacheability.NoCache);
            context.Response.BufferOutput = true;
            context.Response.Flush();
            objBitmap.Save(context.Response.OutputStream, ImageFormat.Jpeg);
        }
            
        HttpApplication app = context.ApplicationInstance;
 
        //you can use the following two setence to create a unique 
        //GUID to access the newly-generated verfying code
        //here we simply hard code it
        //Guid guid = System.Guid.NewGuid();
        // string strGuid = guid.ToString();
        string strGuid = "CAPTCHA";
 
        if (strGuid != String.Empty)
        {
            HttpRuntime.Cache.Insert(strGuid, _randomText);
        }
    }    
}

<asp:Panel ID="popPanel1" runat="server" Height="233px" Width="341px" 
    CssClass="confirmPanel" BorderStyle="Inset" BackColor="#CCCCFF" 
    BorderColor="#CCCCFF" Style="display:none" >
    <div id="titleDiv" 
            style="background-color: #6666FF; color: #0000FF; font-weight: bold; 
font-size: 20px; background-image: url('images/formback.GIF'); 
background-repeat: repeat;">Warning</div>
    <div align='center' style="background-color: #008080; border-style: inset; 
border-color: #800000; height: 179px; text-align: left; font-size: 16px; 
color: #FF0000;" id="bodyDiv">
        Sorry, the nickname, title,content cannot be empty!<br />
        <br />
        Please try again.</div>
    <div style="text-align: center; clip: rect(5px, auto, auto, auto);">
    
    <asp:Button ID="btnOK" runat="server" Text="OK" CssClass="ButtonCss" 
         Width="66px" Height="26px"></asp:Button>
    </div>
</asp:Panel>
<cc1:ModalPopupExtender ID="ModalPopupExtender1" runat="server" Drag="True" 
    DropShadow="True" OkControlID="btnOK" PopupControlID="popPanel1" 
    TargetControlID="btnOK" PopupDragHandleControlID="popPanel1">
</cc1:ModalPopupExtender>

protected void replay_Click(object sender, System.EventArgs e)
{
    Object httpCache = System.Web.HttpRuntime.Cache.Get("CAPTCHA");
    string httpCacheCAPTCHA = "";
 
    
    if (r_nick.Text.Trim() == "" || r_title.Text.ToString().Trim() == "" || 
        r_content.Value.Trim() == "")
    {
        ModalPopupExtender1.Show();
        lblMessage.Text = "";
    }
    else
    {
 
        if (httpCache != null)
            httpCacheCAPTCHA = httpCache.ToString();
 
        if (txtCAPTCHA.Text  == httpCacheCAPTCHA)
        {
            try
            {
                // Insert Item 
                string ST_sql = 
"insert into ST_replay" + 
"(ST_r_nick,ST_r_title,ST_r_content,ST_r_date,ST_n_id) values ('" + 
r_nick.Text.Trim() + "','" + r_title.Text.Trim() + "','" + 
r_content.Value.Trim() + "','"  + System.DateTime.Now + "'," + Request.QueryString["id"] + ")";
                SqlCommand ST_myCmd = new SqlCommand(ST_sql, ST_myConn);
                ST_myConn.Open();
                ST_myCmd.ExecuteNonQuery();
                ST_myConn.Close();
 
                DataListLeft.DataBind();
 
                ST_add_Re();
 
                r_nick.Text = "";
                r_title.Text = "";
                r_content.Value = "";
                txtCAPTCHA.Text = "";
            }
            catch (HttpException ex)
            {
                lblMessage.Text = "Submit error. Cause:br />" + ex.Message;
            }
        }
        else
        {
            lblMessage.Text = "The verifying code is incorrect, please try again!";
            txtCAPTCHA.Text = "";
        }
    }
}