生成image-code的代码如下：

<%@ WebHandler Language="C#" Class="ValidCode" %>using System;using System.Web;using System.Web.Services;using System.Text;using System.Drawing;using System.Drawing.Imaging;using System.Web.SessionState;public class ValidCode : IHttpHandler, IRequiresSessionState, IReadOnlySessionState{        public void ProcessRequest (HttpContext context) {        context.Response.ContentType = "image/gif";            Bitmap basemap = new Bitmap(200, 60);            Graphics garph1 = Graphics.FromImage(basemap);            garph1.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);            Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);            Random r = new Random();            string letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ";            string letter;            StringBuilder s = new StringBuilder();            for (int i = 0; i < 5; i++)            {                letter = letters.Substring(r.Next(0, letters.Length - 1), 1);                s.Append(letter);                garph1.DrawString(letter, font, new SolidBrush(Color.Black), i * 38, r.Next(0, 15));            }            Pen linePen = new Pen(new SolidBrush(Color.Black), 2);            for (int x = 0; x < 6; x++)            {                garph1.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));            }            basemap.Save(context.Response.OutputStream, ImageFormat.Gif);            context.Session["CheckCode"] = s.ToString();    //存入Session，用于对比验证            context.Response.End();    }     public bool IsReusable {        get {            return false;        }    }}

调用代码如下：