asp.net实现图片防盗链

using System;
using System.Collections;
using System.Data;
using System.Web;
using System.Web.Services;
using System.Web.Services.Protocols;
namespace TestSite
{
    /// <summary>
    /// $codebehindclassname$ 的摘要说明
    /// </summary>
    [WebService(Namespace = "http://tempuri.org/")]
    [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
    public class MyUpload : IHttpHandler
    {
        /// <summary>
        /// 重写
        /// </summary>
        /// <param name="context"></param>
        public void ProcessRequest(HttpContext context)
        {
            context.Response.ContentType = "image/jpg";
            if (context.Request.UrlReferrer != null && context.Request.UrlReferrer.Host.Equals(context.Request.Url.Host, StringComparison.InvariantCultureIgnoreCase))
                context.Response.WriteFile(context.Server.MapPath("~/" + context.Request.QueryString["img"]));
            else
                context.Response.WriteFile(context.Server.MapPath("~/logo.jpg"));
        }
        public bool IsReusable
        {
            get
            {
                return true;
            }
        }
    }
}