<table><tr><td style="text-align: right; height: 40px; width: 100px;"><asp:TextBox ID="txtCheckCode" runat="server" Height="25px" Width="97px" ValidationGroup="1"></asp:TextBox></td><td style="text-align: center; height: 40px; width: 100px;"><img id="chkCode" src="CheckCode.aspx" οnclick="javascript:CheckCode();" style="cursor: pointer" /></td><td>&nbsp;<asp:RequiredFieldValidator ID="RequiredFieldValidator2" runat="server" ControlToValidate="txtCheckCode"ErrorMessage="请输入验证码！" ForeColor="Red" ValidationGroup="1"></asp:RequiredFieldValidator></td><td><asp:Button  ID="btn" Text="登陆" runat="server" οnclick="btn_Click" ValidationGroup="1" Style="height: 20px" /><asp:Label ID="zt" ForeColor="Red" runat="server"></asp:Label></td></tr></table>

 <script language="javascript" type="text/javascript" src="./Scripts/jquery-1.4.1.min.js"></script><script language="javascript" type="text/javascript">function CheckCode() {$("#chkCode").attr("src", "./CheckCode.aspx?" + Math.random());}
</script>

 protected void btn_Click(object sender, EventArgs e){string checkCode =txtCheckCode.Text.Trim();string ischeck = Session["UserCCode"].ToString();if (!string.IsNullOrEmpty(checkCode)&& ischeck.Equals(checkCode)){this.zt.Text = "登陆成功！";}else{this.zt.Text = "登陆失败！";}}

using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Drawing;public partial class CheckCode : System.Web.UI.Page
{protected void Page_Load(object sender, EventArgs e){this.CreateCheckCodeImage(GenerateCheckCode());}private string GenerateCheckCode(){int number;char code;string checkCode = String.Empty;Random random = new Random();for (int i = 0; i < 5; i++){number = random.Next();if (number % 2 == 0)code = (char)('0' + (char)(number % 10));elsecode = (char)('A' + (char)(number % 26));checkCode += code.ToString();}//Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));Session["UserCCode"] = 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 * 14.5)), 26);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", 13, (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.DarkTurquoise, 1.2f, true);g.DrawString(checkCode, font, brush, 6, 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();}}
}