验证码问题``

//cs
using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
//Drawing:制图 Imaging:成像
using System.Drawing.Imaging;
using System.IO;public partial class Public_ImageCode : System.Web.UI.Page
{
    // 验证码长度
    private int codeLen = 4;
    // 图片清晰度
    private int fineness = 85;
    // 图片宽度
    private int imgWidth = 55;
    // 图片高度
    private int imgHeight = 20;
    // 字体家族名称
    private string fontFamily = "Arial";//"Times New Roman",
    // 字体大小
    private int fontSize = 14;
    // 字体样式
    private int fontStyle = 3;
    // 绘制起始坐标 X
    private int posX = 2;
    // 绘制起始坐标 Y
    private int posY = 0;    protected void Page_Load(object sender, EventArgs e)
    {
        #region 读取 Request 传递参数
        // 获取代码长度设置
        if (Request["CodeLen"] != null)
        {
            try
            {
                codeLen = Int32.Parse(Request["CodeLen"]);                // 规定验证码长度
                if (codeLen < 4 || codeLen > 16)
                    throw new Exception("验证码长度必须在4到16之间");
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 获取图片清晰度设置
        if (Request["Fineness"] != null)
        {
            try
            {
                fineness = Int32.Parse(Request["Fineness"]);                // 验证清晰度
                if (fineness < 0 || fineness > 100)
                    throw new Exception("图片清晰度必须在0到100之间");
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 获取图片宽度
        if (Request["ImgWidth"] != null)
        {
            try
            {
                imgWidth = Int32.Parse(Request["ImgWidth"]);                if (imgWidth < 16 || imgWidth > 480)
                    throw new Exception("图片宽度必须在16到480之间");
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 获取图片高度
        if (Request["ImgHeight"] != null)
        {
            try
            {
                imgWidth = Int32.Parse(Request["ImgHeight"]);                if (imgWidth < 16 || imgWidth > 320)
                    throw new Exception("图片高度必须在16到320之间");
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 获取验证码字体家族名称
        if (Request["FontFamily"] != null)
        {
            fontFamily = Request["FontFamily"];
        }        // 获取验证码字体大小
        if (Request["FontSize"] != null)
        {
            try
            {
                fontSize = Int32.Parse(Request["FontSize"]);                if (fontSize < 8 || fontSize > 72)
                    throw new Exception("字体大小必须在8到72之间");
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 获取字体样式
        if (Request["FontStyle"] != null)
        {
            try
            {
                fontStyle = Int32.Parse(Request["FontStyle"]);
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 验证码绘制起始位置 X
        if (Request["PosX"] != null)
        {
            try
            {
                posX = Int32.Parse(Request["PosX"]);
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }        // 验证码绘制起始位置 Y
        if (Request["PosY"] != null)
        {
            try
            {
                posY = Int32.Parse(Request["PosY"]);
            }
            catch (Exception Ex)
            {
                throw Ex;
            }
        }
        #endregion        string validateCode = CreateValidateCode();        // 生成BITMAP图像
        Bitmap bitmap = new Bitmap(imgWidth, imgHeight);        // 给图像设置干扰
        DisturbBitmap(bitmap);        // 绘制验证码图像
        DrawValidateCode(bitmap, validateCode);        // 保存验证码图像，等待输出
        bitmap.Save(Response.OutputStream, ImageFormat.Gif);
    }    //------------------------------------------------------------
    // 随机生成验证码并生成Session
    //------------------------------------------------------------
    private string CreateValidateCode()
    {
        string validateCode = "";        // 随机数对象
        Random random = new Random();
        for (int i = 0; i < codeLen; i++)
        {
            // 26: a - z
            //int n=random.Next(26);
            int n = random.Next(10);            // 将数字转换成大写字母
            validateCode += (char)(n + 48);
            //validateCode += (char)(n+97);
        }
        //生成Session["ImageCode"]
        Session["ImageCode"] = validateCode;        return validateCode;
    }    //------------------------------------------------------------
    // 为图片设置干扰点
    //------------------------------------------------------------
    private void DisturbBitmap(Bitmap bitmap)
    {
        // 通过随机数生成
        Random random = new Random();        for (int i = 0; i < bitmap.Width; i++)
        {
            for (int j = 0; j < bitmap.Height; j++)
            {
                if (random.Next(100) <= this.fineness)
                    bitmap.SetPixel(i, j, Color.White);
            }
        }
    }    //------------------------------------------------------------
    // 绘制验证码图片
    //------------------------------------------------------------
    private void DrawValidateCode(Bitmap bitmap, string validateCode)
    {
        // 获取绘制器对象
        Graphics g = Graphics.FromImage(bitmap);        // 设置绘制字体
        Font font = new Font(fontFamily, fontSize, GetFontStyle());        // 绘制验证码图像
        g.DrawString(validateCode, font, Brushes.Black, posX, posY);
    }    //------------------------------------------------------------
    // 换算验证码字体样式：1 粗体 2 斜体 3 粗斜体，默认为普通字体
    //------------------------------------------------------------
    private FontStyle GetFontStyle()
    {
        if (fontStyle == 1)
            return FontStyle.Bold;
        else if (fontStyle == 2)
            return FontStyle.Italic;
        else if (fontStyle == 3)
            return FontStyle.Bold | FontStyle.Italic;
        else
            return FontStyle.Regular;
    }}//aspx<%@ Page Language="C#" AutoEventWireup="true" CodeFile="ImageCode.aspx.cs" Inherits="Public_ImageCode" %><%
Response.Expires = 0;
Response.ExpiresAbsolute = DateTime.Now.AddDays(-1);
Response.AddHeader("pragma","no-cache");
Response.AddHeader("cache-control","private");
Response.CacheControl = "no-cache";
%>