给大家看一段asp.net代码，解决一个小问题


using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
namespace WebApplication_Charge.Pages
{
    public partial class Login_User : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
                CreateCheckCodeImage(GenerateCheckCode());
        }        /// <summary>
        /// 生成随机字母数字
        /// </summary>
        /// <returns></returns>
        private string GenerateCheckCode()
        {
            int number;
            char code;
            string checkCode = String.Empty;            System.Random random = new Random();            for (int i = 0; i < 5; i++)
            {
                number = random.Next(); //Random.Next 方法 () 返回非负随机数。                 if (number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('A' + (char)(number % 26));                checkCode += code.ToString();
            }            Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));            return checkCode;
        }        /// <summary>
        /// 生成背景图像
        /// </summary>
        /// <param name="checkCode"></param>
        private void CreateCheckCodeImage(string checkCode)
        {
            if (checkCode == null || checkCode.Trim() == String.Empty)
                return;            System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
            Graphics g = Graphics.FromImage(image);            try
            {
                //生成随机生成器
                Random random = new Random();                //清空图片背景色
                g.Clear(Color.White);                //画图片的背景噪音线
                for (int i = 0; i < 25; i++)
                {
                    int x1 = random.Next(image.Width);
                    int x2 = random.Next(image.Width);
                    int y1 = random.Next(image.Height);
                    int y2 = random.Next(image.Height);                    g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }                Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
                System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                g.DrawString(checkCode, font, brush, 2, 2);                //画图片的前景噪音点
                for (int i = 0; i < 100; i++)
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }                //画图片的边框线
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();
                Response.ContentType = "image/Gif";
                Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }
    }
}
我在前台.aspx中这样调用的
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Login_User.aspx.cs" Inherits="WebApplication_Charge.Pages.Login_User" %><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title></title>
</head>
<body bgcolor="">
    <form id="form1" runat="server">
        <table width="100%" height="100%">
            <tr>
                <td>Mail</td>
                <td><asp:TextBox ID="TextBox3" runat="server"></asp:TextBox></td>
            </tr>
            
            <tr>
                <td><asp:TextBox ID="TextBox1" runat="server"></asp:TextBox></td>
                <td>
                    <img src="Login_User.aspx" border="0"/>
                </td>
            </tr>
        </table>
    </form>
</body>
</html>
问题是，到前台刷出来的页面，只有一个图片，其他html标签都没出来，怎么回事，求大神解答