Asp.Net验证码

验证码：<input name="txtCode0" type="text" id="txtCode0" class="login-text" size="10" maxlength="4">
<img src="CodeHandler.ashx" id="imgCode" alt="验证码" title="点击刷新验证码" align="middle"
                                    style="height: 24px; width: 70px;" onclick="refreshRandCode()">

//刷新验证码
        function refreshRandCode() {
            $(‘#imgCode‘).hide().attr(‘src‘,
            ‘CodeHandler.ashx?‘ + Math.floor(Math.random() * 100)).fadeIn();
        }

Session["checkCode"]　　

<%@ WebHandler Language="C#" Class="CodeHandler" %>

using System;
using System.Web;
using System.Drawing;

public class CodeHandler : IHttpHandler, System.Web.SessionState.IRequiresSessionState{

    public string charSet = "0,1,2,3,4,5,6,8,9,A,B,C,D,E,F,G,H,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z";
    public void ProcessRequest (HttpContext context) {
        string validateCode = CreateRandomCode(4);
        context.Session["checkCode"] = validateCode;
        CreateImage(validateCode, context);   
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }

    /// <summary>    
    /// 生成验证码          
    /// <param name="n">位数</param>   
    /// <returns>验证码字符串</returns>   
    private string CreateRandomCode(int n)
    {
        string[] CharArray = charSet.Split(‘,‘);
        string randomCode = "";
        int temp = -1;
        Random rand = new Random();
        for (int i = 0; i < n; i++)
        {
            if (temp != -1)
            {
                rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
            } int t = rand.Next(CharArray.Length - 1);
            if (temp == t)
            {
                return CreateRandomCode(n);
            } temp = t;
            randomCode += CharArray[t];
        }
        return randomCode;
    }
    private void CreateImage(string checkCode, HttpContext context)
    {
        int iwidth = (int)(checkCode.Length * 14+10);
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);
        Graphics g = Graphics.FromImage(image);
        Font f = new System.Drawing.Font("Arial", 14, (System.Drawing.FontStyle.Italic | System.Drawing.FontStyle.Bold));        // 前景色        
        Brush b = new System.Drawing.SolidBrush(Color.Black);        // 背景色       
        g.Clear(Color.White);        // 填充文字        
        g.DrawString(checkCode, f, b, 0, 1);        // 随机线条        
        Pen linePen = new Pen(Color.Gray, 0); 
        Random rand = new Random();
        for (int i = 0; i < 10; i++)
        {
            int x1 = rand.Next(image.Width);
            int y1 = rand.Next(image.Height);
            int x2 = rand.Next(image.Width);
            int y2 = rand.Next(image.Height);
            g.DrawLine(linePen, x1, y1, x2, y2);
        }        // 随机点        
        for (int i = 0; i < 50; i++)
        {
            int x = rand.Next(image.Width);
            int y = rand.Next(image.Height);
            image.SetPixel(x, y, Color.Gray);
        }        // 边框       
        g.DrawRectangle(new Pen(Color.Gray), 0, 0, image.Width - 1, image.Height - 1);        // 输出图片  
        System.IO.MemoryStream ms = new System.IO.MemoryStream();
        image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
        context.Response.ClearContent();
        context.Response.ContentType = "image/Jpeg";
        context.Response.BinaryWrite(ms.ToArray());
        g.Dispose();
        image.Dispose();
    }    

}