C#验证码的生成

<ul>
   <li>验证码：</li>
   <li>
    <img src="/Login/GetValidateCode?ID=1" id="imgCode" alt="单击刷新" onclick="ClickChangeCode()"  />
    <a href="javascript:void(0)" onclick="ClickChangeCode();return false;">看不清</a>
   </li>
</ul>

<script type="text/javascript">
    function ClickChangeCode() {
        var code = $("#imgCode").attr("src");
        $("#imgCode").attr("src", code + "1");
    }
</script>

public class ValidateCode
{
    public int MaxLength
    {
        get { return 10; }
    }
    public int MinLength
    {
        get { return 1; }
    }
    //生成验证码
    public string CreateValidateCode(int length)
    {
        int[] randMembers = new int[length];
        int[] validateNums = new int[length];
        string validateNumberStr = "";
        //生成起始序列值
        int seekSeek = unchecked((int) DateTime.Now.Ticks);
        Random seekRand = new Random(seekSeek);
        int beginSeek = (int) seekRand.Next(0, Int32.MaxValue - length*10000);
        int[] seeks = new int[length];
        for (int i = 0; i < length; i++)
        {
            beginSeek += 10000;
            seeks[i] = beginSeek;
        }
        //生成随机数字
        for (int i = 0; i < length; i++)
        {
            Random rand = new Random(seeks[i]);
            int pownum = 1*(int) Math.Pow(10, length);
            randMembers[i] = rand.Next(pownum, Int32.MaxValue);
        }
        //抽取随机数字
        for (int i = 0; i < length; i++)
        {
            string numStr = randMembers[i].ToString();
            int numLength = numStr.Length;
            Random rand = new Random();
            int numPosition = rand.Next(0, numLength - 1);
            validateNums[i] = Int32.Parse(numStr.Substring(numPosition, 1));
        }
        //生成验证码
        for (int i = 0; i < length; i++)
        {
            validateNumberStr += validateNums[i].ToString();
        }
        return validateNumberStr;
    }
    //生成验证码的图片
    public byte[] CreateValidateGraphic(string validateCode)
    {
        Bitmap image = new Bitmap((int) Math.Ceiling(validateCode.Length*12.0), 22);
        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);
            //画图片的干扰线
            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 Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));
            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height),
　　　　　　　　　　　　　　　　　　　　　　　　　　Color.Blue, Color.DarkRed, 1.2f, true);
            g.DrawString(validateCode, font, brush, 3, 2);
            //画图片的前景干扰点
            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);
            //保存图片数据
            MemoryStream stream = new MemoryStream();
            image.Save(stream, ImageFormat.Jpeg);
            //输出图片流
            return stream.ToArray();
        }
        finally
        {
            g.Dispose();
            image.Dispose();
        }
    }
    //得到验证码图片的长度
    public static int GetImageWidth(int validateNumLength)
    {
        return (int) (validateNumLength*12.0);
    }
    // 得到验证码的高度
    public static double GetImageHeight()
    {
        return 22.5;
    }

}

public ActionResult CheckCode()
{
    //首先实例化验证码的类
    ValidateCode validateCode = new ValidateCode();
    //生成验证码指定的长度
    string code = validateCode.CreateValidateCode(5);
    //将验证码赋值给Session变量
    Session["ValidateCode"] = code;
    //创建验证码的图片
    byte[] bytes = validateCode.CreateValidateGraphic(code);
    //最后将验证码返回
    return File(bytes, @"image/jpeg");
}