public enum SubmitCodeMode
{
   Charater = 0,
   Number = 1,
   MixedMode = 2
}

public class SubmitCoder
{
   private Font _CodeFont;
   private Size _CodeImageSize = new Size();
   private SubmitCodeMode _Mode = SubmitCodeMode.MixedMode;
   
   public SubmitCoder(Size codeImageSize, SubmitCodeMode mode, Font codeFont)
   {
      _CodeFont = codeFont;
      _CodeImageSize = codeImageSize;
      _Mode = mode;
   }
   
   /// <summary>
   /// build sumbitcode character
   /// </summary>
   public string GenerateCheckCode()
   {
      int CODE_LENGTH = 5;
      int number;
      char code;
      string checkCode = String.Empty;
      
      System.Random random = new Random();
      int count = 1;
      while (true)
      {
         number = random.Next();
         
         if (_Mode == SubmitCodeMode.MixedMode)
         {
            if (number % 2 == 0)
            code = (char)(’0’ + (char)(number % 10));
            else
            code = (char)(’A’ + (char)(number % 26));
         }
         else if (_Mode == SubmitCodeMode.Number)
         code = (char)(’0’ + (char)(number % 10));
         else if (_Mode == SubmitCodeMode.Charater)
         code = (char)(’A’ + (char)(number % 26));
         else continue;
         checkCode += code.ToString();
         count += 1;
         if (count > CODE_LENGTH) break;
      }
      return checkCode;
   }
   
   /// <summary>
   /// build picture
   /// </summary>
   /// <param name="checkCode"></param>
   public Image BuildSumbitCodeImage(string checkCode)
   {
      //System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 36);
      System.Drawing.Bitmap image = new Bitmap(_CodeImageSize.Width, _CodeImageSize.Height);
      Graphics g = Graphics.FromImage(image);
      try
      {
         //build random number
         Random random = new Random();
         
         //clean picture backcolor
         g.Clear(Color.White);
         
         //draw picture background yamp line
         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", _CodeFont.Size, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
         //Font font = _CodeFont;
         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);
         
         //draw picutre foregound yamp dot
         for (int i = 0; i < 100; i++)
         {
            int x = random.Next(image.Width);
            int y = random.Next(image.Height);
         }
         
         //draw picture boderline
         g.DrawRectangle(new Pen(Color.Green), 0, 0, image.Width - 1, image.Height - 1);
         
         System.IO.MemoryStream ms = new System.IO.MemoryStream();
         image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
         System.IO.Stream sr = ms;
         return System.Drawing.Image.FromStream(sr, true, true);
      }
      finally
      {
         g.Dispose();
         image.Dispose();
      }
   }
}