生成数字验证码

 protected void Page_Load(object sender, EventArgs e)
    {
        string[] str = new string[4];
        string serverCode = "";
        //生成随机数
        Random random = new Random();
        for (int i = 0; i < 4; i++)
        {
            str[i] = random.Next(10).ToString().Substring(0, 1);
        }
        CreateCheck(str);
        foreach (string s in str)
        {
            serverCode += s;
        }

　　　Session["serverCoder"] = serverCode; //将验证码放入session中便于页面调用比较。
    }

    //创建验证码
    private void CreateCheck(string[] strCheck)
    {
        if (strCheck == null || strCheck.Length == 0)
        {
            return;
        }
        else
        {
            //得到要生成的字符，并创建图片
            System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling(strCheck.Length * 32.5),30);
            System.Drawing.Graphics gra = System.Drawing.Graphics.FromImage(image);

            try
            {
                Random random = new Random();
                gra.Clear(System.Drawing.Color.White);//清空图片的背景颜色，并创建新的颜色
                //画出图片的噪音线
                for (int i = 0; i < 20; 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);
                    gra.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);

                }
                // 自定义颜色
                Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
                //定义字体
                string[] f = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };

                for (int k = 0; k <= strCheck.Length-1; k++)
                {
                    int cindex = random.Next(7);
                    int findex = random.Next(5);
                    Font drawFont = new Font(f[findex], 16, (System.Drawing.FontStyle.Bold));
                    SolidBrush drawBrush = new SolidBrush(c[cindex]);
                    float x = 5.0F;
                    float y = 0.0F;
                    float width = 20.0F;
                    float height = 25.0F;
                    int sjx = random.Next(10);
                    int sjy = random.Next(image.Height - (int)height);

                    RectangleF drawRect = new RectangleF(x + sjx + (k * 25), y + sjy, width, height);

                    StringFormat drawFormat = new StringFormat();
                    drawFormat.Alignment = StringAlignment.Center;
                    gra.DrawString(strCheck[k], drawFont, drawBrush, drawRect, drawFormat);
                }

                //画图片的前景噪音
                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
                gra.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
            {
                gra.Dispose();
                image.Dispose();
            }
        }
    }