在登陆框中，用一个图片控件：

　　　　　　　　　　
     
 
      验证码： 
       
       
     

GetCheckCode是JS事件，用来手动刷新验证码：

function GetCheckCode() {
       document.getElementById("imgCode").src = "CheckCode.aspx"; }

 

最好，来到重要的验证码生成页面。由上面的引用已经可以看到，CheckCode.aspx是一个页面，而且这个页面的主要职责就是输出一个位图图象。PS.这个页面的前端代码没有任何额外的，就是新建时的默认。

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.UI; using System.Web.UI.WebControls; using System.Drawing; namespace KeySystem {
   public partial class CheckCode : System.Web.UI.Page     {
   protected void Page_Load(object sender, EventArgs e)         {
               CreateCheckCodeImage(GenerateCheckCode());// 页面加载时调用方法绘制验证码         } private string GenerateCheckCode()         {
   int number; char code; string checkCode = string.Empty;             Random random = new Random(); for (int i = 0; i < 4; i++)             {
                   number = random.Next();                 code =(char)('0'+(char)(number % 10));                 checkCode += code.ToString();             }             Response.Cookies.Add(new HttpCookie("CheckCode", checkCode)); return checkCode;         } private void CreateCheckCodeImage(string checkCode)         {
   if (checkCode == null || checkCode.Trim() == String.Empty) return; //开始创建一个位图             System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling(checkCode.Length * 12.5), 22);             Graphics g = Graphics.FromImage(image); try             {
                   Random random = new Random();                 g.Clear(Color.White); for (int i = 0; i < 2; i++)//图片背景噪音线                 {
   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.Black), x1, y1, x2, y2);                 }                 Font font = new System.Drawing.Font("Arial", 12, System.Drawing.FontStyle.Bold);                 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,Brushes.Black,2,2);//绘制文字 //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()));                 } //图片的边框线                 g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); //输出                 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();             }         }     } }