验证码ValidateCode

public partial class ValidateCode : System.Web.UI.Page
    {
        /// <summary>
        /// Validation Code generated fromt these charaters.
        /// Note: l,L 1(number), o, O, 0(number) are removed
        /// </summary>
        private const string strValidateCodeBound = "abcdefghijkmnpqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ23456789";
        private static string[] Fonts = new string[] {  "Helvetica",
                                                  "Geneva",
                                                  "sans-serif",
                                                  "Verdana",
                                                  "Times New Roman",
                                                  "Courier New",
                                                  "Arial"
                                              };
        #region Web Form Designer generated code

        protected override void OnInit(EventArgs e)
        {
            //
            // CODEGEN: This call is required by the ASP.NET Web Form Designer.
            //
            InitializeComponent();
            base.OnInit(e);
        }

        /// <summary>
        /// Required method for Designer support - do not modify
        /// the contents of this method with the code editor.
        /// </summary>
        private void InitializeComponent()
        {
            this.Load += new System.EventHandler(this.Page_Load);

        }
        #endregion
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                string str_ValidateCode = GetRandomString(6);

                Session["ValidateCode"] = str_ValidateCode;
                CreateImage(str_ValidateCode);
            }
        }
        /// <summary>
        /// Generate random string
        /// </summary>
        private string GetRandomString(int int_NumberLength)
        {
            try
            {
                string valString = string.Empty;
                Random theRandomNumber = new Random((int)DateTime.Now.Ticks);

                for (int int_index = 0; int_index < int_NumberLength; int_index++)
                    valString += strValidateCodeBound[theRandomNumber.Next(strValidateCodeBound.Length - 1)].ToString();

                return valString;
            }
            catch (Exception)
            {             
                return "unknow";
            }
        }
        /// <summary>
        /// Generate random Color
        /// </summary>
        private Color GetRandomColor()
        {
            try
            {
                Random RandomNum_First = new Random((int)DateTime.Now.Ticks);

                System.Threading.Thread.Sleep(RandomNum_First.Next(50));
                Random RandomNum_Sencond = new Random((int)DateTime.Now.Ticks);

                int int_Red = RandomNum_First.Next(256);
                int int_Green = RandomNum_Sencond.Next(256);
                int int_Blue = (int_Red + int_Green > 400) ? 0 : 400 - int_Red - int_Green;
                int_Blue = (int_Blue > 255) ? 255 : int_Blue;

                return Color.FromArgb(int_Red, int_Green, int_Blue);
            }
            catch (Exception)
            {
                throw;
            }
        }
        /// <summary>
        /// Create Validation Code Image
        /// </summary>
        private void CreateImage(string str_ValidateCode)
        {
            try
            {
                int int_ImageWidth = str_ValidateCode.Length * 22;
                Random newRandom = new Random();

                Bitmap theBitmap = new Bitmap(int_ImageWidth + 6, 38);
                Graphics theGraphics = Graphics.FromImage(theBitmap);

                theGraphics.Clear(Color.White);

                drawLine(theGraphics, theBitmap, newRandom);
                theGraphics.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, theBitmap.Width - 1, theBitmap.Height - 1);

                for (int int_index = 0; int_index < str_ValidateCode.Length; int_index++)
                {
                    Matrix X = new Matrix();
                    X.Shear((float)newRandom.Next(0, 300) / 1000 - 0.25f, (float)newRandom.Next(0, 100) / 1000 - 0.05f);
                    theGraphics.Transform = X;
                    string str_char = str_ValidateCode.Substring(int_index, 1);
                    System.Drawing.Drawing2D.LinearGradientBrush newBrush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, theBitmap.Width, theBitmap.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                    Point thePos = new Point(int_index * 21 + 1 + newRandom.Next(3), 1 + newRandom.Next(13));
                    Font theFont = new Font(Fonts[newRandom.Next(Fonts.Length - 1)], newRandom.Next(14, 18), FontStyle.Bold);
                    theGraphics.DrawString(str_char, theFont, newBrush, thePos);
                }

                drawPoint(theBitmap, newRandom);

                MemoryStream ms = new MemoryStream();
                theBitmap.Save(ms, ImageFormat.Png);

                Response.ClearContent();
                Response.ContentType = "image/Png";
                Response.BinaryWrite(ms.ToArray());
                theGraphics.Dispose();
                theBitmap.Dispose();
                Response.End();
            }
            catch (Exception)
            {              
                throw;
            }
        }
        /// <summary>
        /// Draw Line for noise
        /// </summary>
        private void drawLine(Graphics gfc, Bitmap img, Random ran)
        {
            try
            {
                for (int i = 0; i < 10; i++)
                {
                    int x1 = ran.Next(img.Width);
                    int y1 = ran.Next(img.Height);
                    int x2 = ran.Next(img.Width);
                    int y2 = ran.Next(img.Height);
                    gfc.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }
            }
            catch (Exception)
            {              
                throw;
            }
        }
        /// <summary>
        /// Draw Point for noise
        /// </summary>
        private void drawPoint(Bitmap img, Random ran)
        {
            try
            {
                for (int i = 0; i < 30; i++)
                {
                    int x = ran.Next(img.Width);
                    int y = ran.Next(img.Height);
                    img.SetPixel(x, y, Color.FromArgb(ran.Next()));
                }
            }
            catch (Exception)
            { 
                throw;
            }

        }
    }