网页验证码 书写

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

using System;
using System.Web;
using System.Drawing;
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();
        }
        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;
        }
    }

}