public class ValidCode
{
  #region Private Fields
  private const double PI = 3.1415926535897932384626433832795;
  private const double PI2 = 6.283185307179586476925286766559;
  //private readonly int _wordsLen = 4;
  private int _len;
  private CodeType _codetype;
  private readonly Single _jianju = (float)18.0;
  private readonly Single _height = (float)24.0;
  private string _checkCode;
  #endregion
  #region Public Property
  public string CheckCode
  {
   get
   {
    return _checkCode;
   }
  }
  #endregion
  #region Constructors
  /// <summary>
  /// public constructors
  /// </summary>
  /// <param name="len"> 驗(yàn)證碼長度 </param>
  /// <param name="ctype"> 驗(yàn)證碼類型：字母、數(shù)字、字母+ 數(shù)字 </param>
  public ValidCode(int len, CodeType ctype)
  {
   this._len = len;
   this._codetype = ctype;
  }
  #endregion
  #region Public Field
  public enum CodeType { Words, Numbers, Characters, Alphas }
  #endregion
  #region Private Methods
  private string GenerateNumbers()
  {
   string strOut = "";
   System.Random random = new Random();
   for (int i = 0; i < _len; i++)
   {
    string num = Convert.ToString(random.Next(10000) % 10);
    strOut += num;
   }
   return strOut.Trim();
  }
  private string GenerateCharacters()
  {
   string strOut = "";
   System.Random random = new Random();
   for (int i = 0; i < _len; i++)
   {
    string num = Convert.ToString((char)(65 + random.Next(10000) % 26));
    strOut += num;
   }
   return strOut.Trim();
  }
  //
  private string GenerateAlphas()
  {
   string strOut = "";
   string num = "";
   System.Random random = new Random();
   for (int i = 0; i < _len; i++)
   {
    if (random.Next(500) % 2 == 0)
    {
     num = Convert.ToString(random.Next(10000) % 10);
    }
    else
    {
     num = Convert.ToString((char)(65 + random.Next(10000) % 26));
    }
    strOut += num;
   }
   return strOut.Trim();
  }
  private System.Drawing.Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
  {
   System.Drawing.Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
   // 將位圖背景填充為白色
   System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(destBmp);
   graph.FillRectangle(new SolidBrush(System.Drawing.Color.White), 0, 0, destBmp.Width, destBmp.Height);
   graph.Dispose();
   double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;
   for (int i = 0; i < destBmp.Width; i++)
   {
    for (int j = 0; j < destBmp.Height; j++)
    {
     double dx = 0;
     dx = bXDir ? (PI2 * (double)j) / dBaseAxisLen : (PI2 * (double)i) / dBaseAxisLen;
     dx += dPhase;
     double dy = Math.Sin(dx);
     // 取得當(dāng)前點(diǎn)的顏色
     int nOldX = 0, nOldY = 0;
     nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
     nOldY = bXDir ? j : j + (int)(dy * dMultValue);
     System.Drawing.Color color = srcBmp.GetPixel(i, j);
     if (nOldX >= 0 && nOldX < destBmp.Width
      && nOldY >= 0 && nOldY < destBmp.Height)
     {
      destBmp.SetPixel(nOldX, nOldY, color);
     }
    }
   }
   return destBmp;
  }
  #endregion
  #region Public Methods
  public Stream CreateCheckCodeImage()
  {
   string checkCode;
   switch (_codetype)
   {
    case CodeType.Alphas:
     checkCode = GenerateAlphas();
     break;
    case CodeType.Numbers:
     checkCode = GenerateNumbers();
     break;
    case CodeType.Characters:
     checkCode = GenerateCharacters();
     break;
    default:
     checkCode = GenerateAlphas();
     break;
   }
   this._checkCode = checkCode;
   MemoryStream ms = null;
   //
   if (checkCode == null || checkCode.Trim() == String.Empty)
    return null;
   Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * _jianju)), (int)_height);
   Graphics g = Graphics.FromImage(image);
   try
   {
    Random random = new Random();
    g.Clear(Color.White);
    // 畫圖片的背景噪音線
    for (int i = 0; i < 18; 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.FromArgb(random.Next()), 1), x1, y1, x2, y2);
    }
    Font font = new System.Drawing.Font("Times New Roman", 14, System.Drawing.FontStyle.Bold);
    LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
    if (_codetype != CodeType.Words)
    {
     for (int i = 0; i < checkCode.Length; i++)
     {
      g.DrawString(checkCode.Substring(i, 1), font, brush, 2 + i * _jianju, 1);
     }
    }
    else
    {
     g.DrawString(checkCode, font, brush, 2, 2);
    }
    // 畫圖片的前景噪音點(diǎn)
    for (int i = 0; i < 150; i++)
    {
     int x = random.Next(image.Width);
     int y = random.Next(image.Height);
     image.SetPixel(x, y, Color.FromArgb(random.Next()));
    }
    // 畫圖片的波形濾鏡效果
    if (_codetype != CodeType.Words)
    {
     image = TwistImage(image, true, 3, 1);
    }
    // 畫圖片的邊框線
    g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
    ms = new System.IO.MemoryStream();
    image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
   }
   finally
   {
    g.Dispose();
    image.Dispose();
   }
   return ms;
  }
  #endregion
}

//參數(shù)一：產(chǎn)生幾個字符的驗(yàn)證碼圖片 參數(shù)二：驗(yàn)證碼的形式(數(shù)字、字母、數(shù)字字母混合都有)
ValidCode validCode = new ValidCode(5, ValidCode.CodeType.Alphas);
this.pictureBox2.Image = Bitmap.FromStream(validCode.CreateCheckCodeImage());