.Net发出图片Request请求

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 );
                }