<%@ WebHandler Language="C#" Class="show" %>using System;
using System.Web;
using System.Drawing;//引用
using System.Web.SessionState;//IRequiresSessionState的命名空间public class show : IHttpHandler, IRequiresSessionState
{public void ProcessRequest(HttpContext context){context.Response.ContentType = "image/jpeg";//要输出的类型Bitmap img = new Bitmap(50, 20);//造空白图Graphics gr = Graphics.FromImage(img);//往哪个图上去绘制Font font = new Font("宋体", 12, FontStyle.Bold);//设置字体SolidBrush brush = new SolidBrush(Color.White);//设置刷子gr.FillRectangle(brush, 0, 0, 50, 20);//刷子绘制的形状brush.Color = Color.Red;//颜色string s = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";string str = "";Random rand = new Random();//初始化随机数for (int i = 0; i < 4; i++){int start = rand.Next(62); //生成一个随机的起始位置str += s.Substring(start, 1).ToString();}//需要继承接口context.Session["yanzheng"] = str;gr.DrawString(str, font, brush, 0, 0);//绘制完了图片了//将图片保存，通过response响应流保存
        img.Save(context.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);}public bool IsReusable{get{return false;}}}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;public partial class _Default : System.Web.UI.Page
{protected void Page_Load(object sender, EventArgs e){}protected void Button1_Click(object sender, EventArgs e){string txtyanzheng = TextBox1.Text;if (string.IsNullOrWhiteSpace(txtyanzheng)){}else{string yanzheng = Session["yanzheng"].ToString();  //用Session传值接收过来if (txtyanzheng == yanzheng){Response.Write("<script>alert('注册成功')</script>");}else{Response.Write("<script>alert('验证码不正确')</script>");}}}}