主要功能：无刷新实现对用户名，密码，中文验证码的验证！
技术要点：使用.NEt2005中新接口“ICallbackEventHandler”用asp.net动态生成中文验证码
话不多说，直接看代码，
只要有两个页面 Login.aspx 和
ImageR.aspx
Login.aspx 的代码如下：
<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Login.aspx.cs" Inherits="Login" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head runat="server">
<title>Login</title>
<script language="javascript" type="text/javascript">
var div;
function callback()
>
Login.aspx.cs 的代码如下：这个页面实现自 ICallbackEventHandler
接口
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;
public partial class Login : System.Web.UI.Page, ICallbackEventHandler
ImageR.aspx 页面无内容，主要在ImageR.aspx.cs里
代码如下：
using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
public partial class ImageR: System.Web.UI.Page
的
一是在不了有和人这中大为上个国我以要他时来用们生到作地于出就分对成会可主发年动同工也能下过子说产种面而方后多定行学法所民得经十三之进着等部度家电
力里如水化高自二理起小物现实加量都两体制机当使点从业本去把性好应开它合还因由其些然前外天政四日那社义事平形相全表间样与关各重新线内数正心反你明看
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消构府称太准精值号率族维划选标写存候毛亲快效斯院查江型眼王按格养易置派层片始却专状育厂京识适属圆包火住调满县局照参红细引听该铁价严";
char[] chastr = str.ToCharArray();
// string[] source ={ "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z", "#", "$", "%", "&", "@" };
string code = "";
Random rd = new Random();
int i;
for (i = 0; i < num; i++)
