Asp.Net 动态生成验证码

我们在设计用户登录模块时，经常会用到验证码，可以有效地防止黑客软件的恶意破解，现公开我常用的验证码的源代码，
　　 使用方法：
　　 1、在Web项目中添加一个类，如“CreateImage.cs”，然后将我公布的源代码Copy进去；
　　 2、再新建一个Web窗体，如“Image.aspx”，在Page_Load中加入代码 “CreateImage.DrawImage ();”当然别忘了加上对类的引用哦！！
　　 3、在页面的合适位置上（你想放验证码的位置）上加上如下javascript代码就OK 了，
　　
　　
　　源代码如下：
　　
　　
　　///
    /// 验证码模块
    ///
    public class CreateImage
    {
        public CreateImage() { }
        public static void DrawImage()
        {
            CreateImage img = new CreateImage();
            HttpContext.Current.Session["CheckCode"] = img.RndNum(4);
            img.CreateImages(HttpContext.Current.Session["CheckCode"].ToString());
        }

        ///
        /// 生成验证图片
        ///
        /// 验证字符
        private void CreateImages(string checkCode)
        {
            int iwidth = (int)(checkCode.Length * 13);
            System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);
            Graphics g = Graphics.FromImage(image);
            g.Clear(Color.White);
            //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[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };
            Random rand = new Random();
            //随机输出噪点
            for (int i = 0; i < 50; i++)
            {
                int x = rand.Next(image.Width);
                int y = rand.Next(image.Height);
                g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
            }

            //输出不同字体和颜色的验证码字符
            for (int i = 0; i < checkCode.Length; i++)
            {
                int cindex = rand.Next(7);
                int findex = rand.Next(5);

                Font f = new System.Drawing.Font(font[findex], 10, System.Drawing.FontStyle.Bold);
                Brush b = new System.Drawing.SolidBrush(c[cindex]);
                int ii = 4;
                if ((i + 1) % 2 == 0)
                {
                    ii = 2;
                }
                g.DrawString(checkCode.Substring(i, 1), f, b, 3 + (i * 12), ii);
            }
            //画一个边框
            g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width - 1, image.Height - 1);

            //输出到浏览器
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
            HttpContext.Current.Response.ClearContent();
            //Response.ClearContent();
            HttpContext.Current.Response.ContentType = "image/Jpeg";
            HttpContext.Current.Response.BinaryWrite(ms.ToArray());
            g.Dispose();
            image.Dispose();
        }

        ///
        /// 生成随机的字母
        ///
        /// 生成字母的个数
        /// string
        private string RndNum(int VcodeNum)
        {
            string Vchar = "0,1,2,3,4,5,6,7,8,9";
            string[] VcArray = Vchar.Split(',');
            string VNum = ""; //由于字符串很短，就不用StringBuilder了
            int temp = -1; //记录上次随机数值，尽量避免生产几个一样的随机数

            //采用一个简单的算法以保证生成随机数的不同
            Random rand = new Random();
            for (int i = 1; i < VcodeNum + 1; i++)
            {
                if (temp != -1)
                {
                    rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
                }
                int t = rand.Next(VcArray.Length);
                if (temp != -1 && temp == t)
                {
                    return RndNum(VcodeNum);
                }
                temp = t;
                VNum += VcArray[t];
            }
            return VNum;
        }
    }