生成验证码(混合与数字)

生成登录时的验证码 
在Page_Load中调用
Session["pass"] = GenerateCheckCode();
     this.CreateCheckCodeImage(GenerateCheckCode());


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;
  }
  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
   {
       Random random = new Random();

        g.Clear(Color.White);

       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);

 
    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()));
    }
    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();
   }
  }
生成数字码
public void  ValidateCode(string VNum)
  {
   validateimage = new Bitmap(50, 20, PixelFormat.Format24bppRgb);
   g = Graphics.FromImage(validateimage);

   g.DrawString(VNum, new Font("Comic Sans MS",12),new SolidBrush(Color.White),new PointF(3,0));
   g.FillRectangle(new LinearGradientBrush(new Point(0,0), new Point(110,20), Color.FromArgb(0,0,0,0),Color.FromArgb(255,255,60,40)),0,0,120,30);
   g.Save();
   MemoryStream ms=new MemoryStream();
   validateimage.Save(ms,System.Drawing.Imaging.ImageFormat.Gif);
   Response.ClearContent();
   Response.ContentType="image/gif";
   Response.BinaryWrite(ms.ToArray());
   Response.End();
  }

  private string MakeValidateCode()
  {
   char[] s = new char[]{'0','1', '2','3','4','5','6','7','8','9'};
   string num = "";
   Random r = new Random();
   for(int i = 0; i < 4; i++)
   {
    num += s[r.Next(0, s.Length)].ToString();
   }
   return num;
  }