Global.asax 文件中

        protected void Application_BeginRequest(object sender, EventArgs e)

        {

            //判断当前请求是否是访问 images/文件夹

            if (Request.RawUrl.ToLower().Contains("/images/"))

            {

                Uri referrer = Request.UrlReferrer;

                Uri url = Request.Url;

                if (!CompareURL(url, referrer))

                {

                    //输出盗链图片

                    string path = Request.MapPath("~/images/daolian.gif");

                    Response.WriteFile(path);

                    //结束请求

                    Response.End();

                }

            }

        }

        bool CompareURL(Uri u1, Uri u2)

        {

            return Uri.Compare(u1, u2, UriComponents.HostAndPort, UriFormat.SafeUnescaped, StringComparison.CurrentCultureIgnoreCase) == 0;

        }

转：http://blog.csdn.net/zhangquanok/article/details/10072293