Stream reader = null;                //可能是外部链接                if (imgUrl.ToLower().StartsWith("http://"))                {                    var request = System.Net.WebRequest.Create(imgUrl);                    var response = request.GetResponse();                    reader = response.GetResponseStream();                }                else                {                    reader = new FileStream( System.Web.HttpContext.Current.Server.MapPath( imgUrl ), FileMode.Open );                }