C#生成验证码

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Drawing.Imaging;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;

using System.IO;

namespace Shop
{
    /// <summary>
    /// Summary description for ValidateCode.
    /// </summary>
    public 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
        override protected 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

        /// <summary>
        /// event handler of page load
        /// </summary>
        private void Page_Load(object sender, System.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)
        {
            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;
        }

        /// <summary>
        /// Generate random Color
        /// </summary>
        private Color GetRandomColor()
        {
            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);
        }
        
        /// <summary>
        /// Create Validation Code Image
        /// </summary>
        private void CreateImage(string str_ValidateCode)
        {
            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();
        }

        /// <summary>
        /// Draw Line for noise
        /// </summary>
        private void drawLine(Graphics gfc,Bitmap img, Random ran)
        {
            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);
            }
        }

        /// <summary>
        /// Draw Point for noise
        /// </summary>
        private void drawPoint(Bitmap img, Random ran)
        {
            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()));
            }

        }

    }
}

源链接：http://www.oschina.net/code/snippet_99270_1748