ASP.net 验证码(C#)

public class ValidateCode : System.Web.UI.Page
   {
   private void Page_Load(object sender, System.EventArgs e)
   {
   this.CreateCheckCodeImage(GenerateCheckCode());
   }

   #region web 窗体设计器生成的代码
   override protected void OnInit(EventArgs e)
   {
   //
   // CODEGEN: 该调用是 asp.NET web 窗体设计器所必需的。
   //
   InitializeComponent();
   base.OnInit(e);
   }

   /// <summary>
   /// 设计器支持所需的方法 - 不要使用代码编辑器修改
   /// 此方法的内容。
   /// </summary>
   private void InitializeComponent()
   {
   this.Load += new System.EventHandler(this.Page_Load);
   }
   #endregion

   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();

   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;
   }

   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();
   }
   }
   }
http://www.cnblogs.com/niit007/archive/2006/08/13/475506.html