数字验证码的实现

public partial class ValidateCode : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string validateCode = CreateValidateCode();   //生成验证码
        Bitmap bitmap = new Bitmap(imgWidth, imgHeight);   //生成BITMAP图像
        DisturbBitmap(bitmap);   //图像背景
        DrawValidateCode(bitmap, validateCode);  //绘制验证码图像
        bitmap.Save(Response.OutputStream, ImageFormat.Gif);  //保存验证码图像，等待输出
    }
    //定义变量
    private int codeLen = 4;     //验证码长度
    private int fineness = 85;   //图片清晰度
    private int imgWidth = 58;
    private int imgHeight = 24;
    private string fontFamily = "Times New Roman"; //字体名称
    private int fontSize = 14;
    //private int fontStyle = 0;   //字体样式
    private int posX = 0;        //绘制起始坐标X
    private int posY = 0;        //绘制起始坐标Y

    //随机生成一个验证码的值
    private string CreateValidateCode()
    {
        string validateCode = "";
        Random random = new Random();
        for (int i = 0; i < codeLen; i++)
        {
            int n = random.Next(10);
            validateCode += n.ToString();
        }
        Session["vcode"] = validateCode;
        return validateCode;
    }

    //生成麻点背景效果
    private void DisturbBitmap(Bitmap bitmap)
    {
        Random random = new Random();
        for (int i = 0; i < bitmap.Width; i++)
        {
            for (int j = 0; j < bitmap.Height; j++)
            {
                if (random.Next(90) <= this.fineness)
                {
                    bitmap.SetPixel(i, j, Color.LightGray);
                }
            }
        }
    }

    //将验证码绘制到背景图像上
    private void DrawValidateCode(Bitmap bitmap, string validateCode)
    {
        Graphics g = Graphics.FromImage(bitmap); //获取绘制器对象
        Font font = new Font(fontFamily, fontSize, FontStyle.Bold); //设置绘制字体、
        g.DrawString(validateCode, font, Brushes.Black, posX, posY); //绘制验证码图像
    }
}