无刷新验证码

放验证码的页面内添加如下js脚本，这个是刷新验证码的方法：

<script language="javascript" type="text/javascript">function fresh(){var randomnum=Math.random();var getimagecode=document.getElementById( "codeimage");getimagecode.src= "ValidateImage.aspx? "+randomnum;}</script>

页面内要放验证码的地方（层内，单元格内等）放置如下代码，这个是验证码的图图，输入验证码的文本框和调刷新方法的链接。

<div><img id="codeimage" src="ValidateImage.aspx?,Math.random()" /><asp:TextBox ID="txtValidateCode" runat="server" Width="55px" MaxLength="4"></asp:TextBox><a href="javascript:fresh()" style="font-size: 12px; color: Green">看不清</a></div>

Validateimage.aspx页面是生成图片

 private void Page_Load(object sender, System.EventArgs e)    {        this.CreateCheckCodeImage(RndNum());    }    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;    }    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 < 20; 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.Aqua), 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.BlueViolet, Color.BlueViolet, 1.2f, true);            g.DrawString(checkCode, font, brush, 2, 2);            //画图片的前景噪音点             for (int i = 0; i < 50; 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();        }    }