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

using System;
using System.Web;
using System.Drawing;
using System.Web.SessionState;
public class BackImage : IHttpHandler,IRequiresSessionState {
    
    public void ProcessRequest (HttpContext context) {
        context.Response.ContentType = "image/jpeg";//规定返回一个图片
        //生成一个验证码
        string strCheck = "";
        Random r = new Random();
        for (int i = 1; i <= 4; i++)
        {
            string s = "1234567890abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
            int start = r.Next(61);
            strCheck += s.Substring(start, 1);
        }
        //将验证码画在图片上
        Bitmap img = new Bitmap(40,20);//造一个空白画板
        Graphics gr=Graphics.FromImage(img);//定义一个画板img的画笔
        SolidBrush brush=new SolidBrush(Color.White);//定义一个白色的刷子
        gr.FillRectangle(brush, 0, 0, 40, 20); //画一个白色长方形背景
        
        Font font=new Font("宋体",13,FontStyle.Italic);//定义一个绘制字符串时，用的字体
        brush.Color = Color.Red;//改变刷子的颜色，与背景区别
        gr.DrawString(strCheck,font,brush,0,0);

        //将此图像保存到指定的流中
        img.Save(context.Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);

        //定义一个Session传递数据
        context.Session["strCheck"] = strCheck;
    }
 
    public bool IsReusable {
        get {
            return false;
        }
    }

}