1、创建ValidCode类：

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        /// 
         /// public constructors         /// 
         ///  验证码长度          ///  验证码类型：字母、数字、字母+ 数字          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);            // 将位图背景填充为白色             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);                    // 取得当前点的颜色                     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);                // 画图片的背景噪音线                 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);                }                // 画图片的前景噪音点                 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()));                }                // 画图片的波形滤镜效果                 if (_codetype != CodeType.Words)                {                    image = TwistImage(image, true, 3, 1);                }                // 画图片的边框线                 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    }

2、产生验证码图片代码：

//参数一：产生几个字符的验证码图片  参数二：验证码的形式(数字、字母、数字字母混合都有)ValidCode validCode = new ValidCode(5, ValidCode.CodeType.Alphas);

this.pictureBox2.Image = Bitmap.FromStream(validCode.CreateCheckCodeImage());