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#region  ASP.NET 图片验证码
  public 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;
  }
  
  public 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.Buffer = true;
    Response.ClearContent();
    Response.ContentType = "image/Gif";
    Response.BinaryWrite(ms.ToArray());
   }
   finally {
    g.Dispose();
    image.Dispose();
   }
  }
  #endregion