基于ASP.NET实现验证码生成详解

<asp:Label ID="Label1" runat="server" Text="请输入验证码:"  ></asp:Label>
<asp:TextBox ID="tbx_check" runat="server"></asp:TextBox>
<asp:ImageButton ID="ImageButton1" runat="server" src="checknumber.ashx" alt="验证码"/>
<asp:Button ID="btn_check" runat="server" Text="验证" OnClick="btn_check_Click" />

protected void btn_check_Click(object sender, EventArgs e)
{
  //不区分大小写验证
      if (String.Compare(tbx_check.Text.Trim(), Session["check"].ToString(), true) == 0)
      {    
          Response.Write("<script>alert('验证码正确') </script>");
                
      }    
      else
      {
          Response.Write("<script>alert('验证码错误') </script>");
      }
}
 
 
//点击图片更换验证码
protected void ImageButton1_Click(object sender, ImageClickEventArgs e)
{
    ImageButton1.ImageUrl = "checknumber.ashx?id=" + new Random(100).ToString();
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
//画板
using System.Drawing;
using System.Drawing.Imaging;
//Session传值
using System.Web.SessionState;
 
namespace 验证码模块
{
    /// <summary>
    /// Handler1 的摘要说明
    /// </summary>
    public class Handler1 : IHttpHandler, IRequiresSessionState
    {
 
        public void ProcessRequest(HttpContext context)
        {
            
            //定义位图的宽度和高度
            int iBmpW = 200;
            int iBmpS = 50;
 
            //创建位图对象（并初始化宽度和高度）
            Bitmap Bmp = new Bitmap(iBmpW, iBmpS);
 
            //创建画布
            Graphics Grc = Graphics.FromImage(Bmp);//将位图装载到画布里面
 
            //将画布的背景色改为白色
            Grc.Clear(Color.White);
 
            //定义画笔对象
            SolidBrush solidBrush = new SolidBrush(Color.Blue);
 
            //定义存放的字符串，画布上要显示的验证码,回避相似字符所以去掉I、1、o、0
            string sString = "ABCDEFGHJKLMNPQRSTUVWXYZabcdefghyzklmnopqrstuvwxtz23456789呆锅工酱";
            //定义随机数
            Random Rnd = new Random((int)DateTime.Now.Ticks);//强制转换为整型
 
            //for存放随机数的字符变量
            string scode = null;
            for (int i = 0; i < 6; i++)
            {
                string temp = sString.Substring(Rnd.Next(0, sString.Length), 1);//将随即得到的每个字符进行字符串构造
                scode += temp;
            }
 
 
            //随机输出噪点
            Random rand = new Random();
            for (int i = 0; i < 10; i++)
            {
                int x = rand.Next(Bmp.Width);
                int y = rand.Next(Bmp.Height);
                Grc.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
            }
 
 
            int z = 6;//干扰线条数
            for (int i = 0; i < z; i++)
            {
                int x1 = rand.Next(Bmp.Width);
                int x2 = rand.Next(Bmp.Width);
                int y1 = rand.Next(Bmp.Height);
                int y2 = rand.Next(Bmp.Height);
                Grc.DrawLine(new Pen(Color.LightGray, 1), x1, y1, x2, y2);//根据坐标画线
            }
 
 
            Font ft = new Font("Arial", 25);
            Grc.DrawString(scode, ft, solidBrush, 0, 0);
            context.Response.ContentType = "image/jpg";
            Bmp.Save(context.Response.OutputStream, ImageFormat.Jpeg);
            //向外传scode的值以验证
            context.Session["check"] = scode;
        }
 
        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }
}