<script language="javascript"> 。

  。

        function changeImg() {             $("#imgCheckNo").attr("src", "ValidateImage.aspx?r=" + getRandom(999));         }         function getRandom(n) { return Math.floor(Math.random() * n + 1) } </script> 。

<div> <img id="imgCheckNo" src="ValidateImage.aspx" style="border-color: #000000; border-width: 1px;border-style: Solid">  <span onclick="changeImg();">看不清?换一张</span>  </div> <div>    <div class="labelCss">验证码：</div> <div> <asp:TextBox ID="tbxCheckNo" runat="server" CssClass="tbxCss"></asp:TextBox> </div> <div> <asp:Button ID="btnSubmit" runat="server" Text="立即注册" OnClick="btnSubmit_Click" /> </div> 。

public partial class ValidateImage : System.Web.UI.Page     {         protected void Page_Load(object sender, EventArgs e)         {             this.CreateCheckCodeImage(RndNum());         } 。

  。

        /// <summary>生成验证码         /// </summary>         /// <returns></returns>         private string RndNum()         {             int number;             char code;             string checkCode = String.Empty,

            System.Random random = new Random(),

            for (int i = 0; i < 4; i++)             {                 number = random.Next();                 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("yzmcode", checkCode));             return checkCode;         } 。

        /// <summary>向页面生成验证码Gif图片         /// </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();             }         } 。

    } 。

#region 页面控件事件
        protected void btnSubmit_Click(object sender, EventArgs e)
        {
            if (String.Compare(Request.Cookies["yzmcode"].Value, tbxCheckNo.Text, true) != 0)
            {
                Response.Write("<script>alert('验证码错误!')</script>");
            }
            else
            {
               // Response.Write("<script>alert('验证吗正确!!!')</script>");
            }
        }
  #endregion