ASP.NET校验码的制着（汉字/字母数字校验码）

闲着没事，在网上看了几个校验码例子，自己做了一下，还可以，现在综合了一下写了下来：
[参照文献(如有侵权，请发邮件以便删除aresmeng@126.com)：
1, 用C#生成随机中文汉字验证码的基本原理
2,FW:网上几种常见校验码图片分析]
汉字校验码：
一，建立一个web窗体Check.aspx
页面加载代码如下:

private void Page_Load(object sender, System.EventArgs e)
        {
            // 在此处放置用户代码以初始化页面
            this.CreateCheckImage(GenerateCheckstring());
        }

加如下方法随机生成汉字:

    private string GenerateCheckstring()
        {
            Encoding e=Encoding.GetEncoding("gb2312");
            object[] yyy=GetObjects(4);
            string firstString=e.GetString((byte[])Convert.ChangeType(yyy[0],typeof(byte[])));
            string secondString=e.GetString((byte[])Convert.ChangeType(yyy[1],typeof(byte[])));
            string thridString=e.GetString((byte[])Convert.ChangeType(yyy[2],typeof(byte[])));
            string fourthString=e.GetString((byte[])Convert.ChangeType(yyy[3],typeof(byte[])));
        
            string CheckSession=firstString+secondString+thridString+fourthString;
            Session["CheckSession"]=CheckSession;

            return Session["CheckSession"].ToString();
        }

        
        private object[] GetObjects(int i)
        {
            //每个汉字都由十六进制组成　如[b2,b3] 二个byte构成一个汉字
            string[] strings=new string[16]{"0","1","2","3","4","5","6","7","8","9","a","b","c","d","e","f"};
            object[] returnbyte=new object[i];
            //Random随机数
            Random rd=new Random();
            //循环产生i个汉字的byte数组
            for(int j=0;j<i;j++)
            {   //第一位十六进制的数
                int byteFirst=rd.Next(11,14);//随机产生第一位byte的数对应的int
                string stringFirstByte=strings[byteFirst].Trim();//取出第一位的那个十六进制数
                //第二位十六进制的数
                rd=new Random(byteFirst*unchecked((int)DateTime.Now.Ticks)+j);//重新生成随机种字，防止重复
                int byteCecond;
                if(byteFirst == 13)//第一位是D的话，第二位区位码就不能是7以后的十六进制数
                {
                    byteCecond=rd.Next(0,7);
                }
                else
                    byteCecond=rd.Next(0,16);
                string stringCecondByte=strings[byteCecond].Trim();
　　　　　　　　//第三位十六进制的数
                rd=new Random(byteCecond*unchecked((int)DateTime.Now.Ticks)+j);
                int byteThrid=rd.Next(10,16);
                string stringThridByte=strings[byteThrid].Trim();
　　　　　　　　//第四位十六进制的数
                rd=new Random(byteThrid*unchecked((int)DateTime.Now.Ticks)+j);
                int byteFourth;
                if(byteThrid == 10)//第3位如果是A的话，第4位就不能是0；第3位如果是F的话，第4位就不能是F
                {
                    byteFourth=rd.Next(1,16);
                }
                else if(byteThrid == 15)
                {
                    byteFourth=rd.Next(0,15);
                }
                else
                {
                    byteFourth=rd.Next(0,16);
                }
                string stringFourthByte=strings[byteFourth].Trim();

                byte firstSection=Convert.ToByte(stringFirstByte+stringCecondByte,16);
                byte cecondSection=Convert.ToByte(stringThridByte+stringFourthByte,16);
                byte[] bytes=new byte[]{firstSection,cecondSection};
                
                returnbyte.SetValue(bytes,j);

            }
            return returnbyte;
        }

加如下方法生成干扰背景：

private void CreateCheckImage(string checkString)
        {
            //判断Session
            if(checkString == null || checkString == String.Empty)
                return;

            System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkString.Length * 23)), 25);
            Graphics g = Graphics.FromImage(image);

            try
            {
                //生成随机生成器
                Random random = new Random();

                //清空图片背景色
                g.Clear(Color.White);

                //画图片的背景噪音线
                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", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
                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(checkString, font, brush, 2, 2);

                //画图片的前景噪音点
                for(int i=0; i<100; i++)
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);

                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }

                //画图片的边框线
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();
                Response.ContentType = "image/Gif";
                Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }

二,在需要页面的html里用<img src="Check.aspx"/>
字母数字校验码

            int number;
            char code;
            string CheckSession = String.Empty;

            System.Random random = new Random();

            for(int i=0; i<5; i++)
            {
                number = random.Next();

                if(number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('A' + (char)(number % 26));

                CheckSession += code.ToString();
            }