asp.net ÑéÖ¤Âë ʵÏÖ

µÚ1ÖÖ.
using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.Drawing;
public partial class fetchcode : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
Random rd = new Random(); //´´½¨Ëæ»úÊý¶ÔÏó
//ÒÔÏÂ4ÐÐ,²úÉúÓÉ6¸ö×ÖĸºÍÊý×Ö×é³ÉµÄÒ»¸ö×Ö·û´®
string str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789ÎÒÄãËû";
string my51aspx = "";
for (int i = 0; i < 4; i++)
{
my51aspx = my51aspx + str.Substring(rd.Next(39), 1);
}
//ÑéÖ¤ÂëÖµ´æ·Åµ½SessionÖÐÓÃÀ´±È½Ï
Session["Valid"] = my51aspx;
//ÒÔÏÂÈý¾ä,ͨ¹ýËæ»úÕÒÒ»¸öÏÖÓÐͼÏó²úÉúÒ»¸ö»­²¼Bitmap
string bgFilePath = Server.MapPath(".\\images\\bg" + new Random().Next(5) + ".jpg");//Ëæ»úÕÒ¸öͼÏó
// string bgFilePath = Server.MapPath(".\\images\\bg2" + ".jpg");//Ëæ»úÕÒ¸öͼÏó
System.Drawing.Image imgObj = System.Drawing.Image.fromFile(bgFilePath);
Bitmap newBitmap = new Bitmap(imgObj, 90, 30);//½¨Á¢Î»Í¼¶ÔÏó
Graphics g = Graphics.fromImage(newBitmap);//¸ù¾ÝÉÏÃæ´´½¨µÄλͼ¶ÔÏó´´½¨»æͼÃæ
Color[] fore = { Color.Black ,Color.Red};
SolidBrush brush = new SolidBrush(fore[new Random().Next(2)]);//ÉèÖû­±ÊÑÕÉ«
//¶¨ÒåÒ»¸öº¬10ÖÖ×ÖÌåµÄÊý×é
String[] fontFamily = { "Arial", "Verdana", "Comic Sans MS", "Impact", "Haettenschweiler", "Lucida Sans Unicode", "Garamond", "Courier New", "Book Antiqua", "Arial Narrow" };
//ͨ¹ýÑ­»·,»æÖÆÿ¸ö×Ö·û,
for (int a = 0; a < my51aspx.Length; a++)
{
Font textFont = new Font(fontFamily[rd.Next(9)], 15, FontStyle.Regular);//×ÖÌåËæ»ú,×ֺŴóС10,¼Ó´Ö
//ÿ´ÎÑ­»·»æÖÆ