搞了半天的结果。。

//system.web下

//HoWave.Web为项目名称，HandlePictrue为 实现类

        <httpHandlers>

            <add verb="*" path="*.php" type="System.Web.UI.PageHandlerFactory" />

      <!--不要被.net处理的类型-->

      <!--<add verb="*" path="*.html,*.jpg,*.jpeg,*.png,*.bmp,*.gif" type="System.Web.DefaultHttpHandler" />-->

      <!--要被.net处理的类型-->

      <add verb="*" path="*.jpg" type="HoWave.Web.HandlePictrue,HoWave.Web" />

      <add verb="*" path="*.jpeg" type="HoWave.Web.HandlePictrue,HoWave.Web" />

      <add verb="*" path="*.png" type="HoWave.Web.HandlePictrue,HoWave.Web" />

      <add verb="*" path="*.bmp" type="HoWave.Web.HandlePictrue,HoWave.Web" />

      <add verb="*" path="*.gif" type="HoWave.Web.HandlePictrue,HoWave.Web" />

        </httpHandlers>

    <system.webServer>

        <defaultDocument>

            <files>

                <add value="index.aspx" />

            </files>

        </defaultDocument>

        <validation validateIntegratedModeConfiguration="false" />

        <handlers>

            <add name=".net40_jpg_tg" path="*" verb="*" type="System.Web.UI.PageHandlerFactory" resourceType="Unspecified" preCondition="integratedMode" />

            <add name=".net40_jpg_tpf" path="*" verb="*" modules="IsapiModule" scriptProcessor="C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" resourceType="Unspecified" requireAccess="None" preCondition="classicMode,runtimeVersionv4.0,bitness32" />

            <add name=".net40_jpg" path="*" verb="*" modules="IsapiModule" scriptProcessor="C:\Windows\Microsoft.NET\Framework\v4.0.30319\aspnet_isapi.dll" resourceType="Unspecified" preCondition="classicMode,runtimeVersionv4.0,bitness32" />

        </handlers>

        <modules>

            <!--<add name="myHandlePictrue" type="HoWave.Web.HandlePictrue,HoWave.Web" preCondition="managedHandler" />-->

        </modules>

    <!--程序池要设置为“经典”模式-->

    </system.webServer>

using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Web;using System.IO;namespace HoWave.Web{    public class HandlePictrue:IHttpHandler    {        public void ProcessRequest(HttpContext context)        {            string requesthost = (context.Request.UrlReferrer == null ? "" : context.Request.UrlReferrer.Host);            string picturehost = context.Request.Url.Host;                        string relationPath = context.Request.FilePath.ToLower();            if (relationPath.EndsWith(".jpg") || relationPath.EndsWith(".jpeg") || relationPath.EndsWith(".png") || relationPath.EndsWith(".bmp") || relationPath.EndsWith(".gif"))            {                context.Response.ContentType = "image/JPEG";                string absolutePath = context.Server.MapPath(context.Request.FilePath);                if (requesthost != picturehost)//盗链，返回提示图片                {                    context.Response.WriteFile("/Img/linknotice/ImageForbiden.jpg");                }                else if (!File.Exists(absolutePath))//图片不存在，返回提示图片                {                    context.Response.WriteFile("/Img/linknotice/ImageNotFound.jpg");                }                else                {                    context.Response.WriteFile(relationPath);                }            }            //else context.RewritePath(relationPath);        }        public bool IsReusable        {            get { return true; }        }           }}