有什么办法可以防止别人拼url地址来访问到服务器上的图片吗？

图片改成有一个ashx输出  
<configSections>
    <section name="rewriter"
         requirePermission="false"
         type="Intelligencia.UrlRewriter.Configuration.RewriterConfigurationSectionHandler, Intelligencia.UrlRewriter" />
  </configSections>  <rewriter>
    <rewrite url="~/(p_img\d{3}/.+?)_(\d{1,3})x(\d{1,3})\.(jpg|jpeg|png|gif|bmp)$"
             to="~/ResponseImg.ashx?FilePath=$1&amp;Width=$2&amp;Height=$3&amp;Hex=$4"/>
  </rewriter>public class ResponseImg : IHttpHandler
    {
        static readonly DateTime Refresh;
        static readonly DateTime Now;
        static ResponseImg()
        {
            Now = DateTime.Now;
            Refresh = Now.AddMonths(1);
        }        public void ProcessRequest(HttpContext context)
        {            if (!string.IsNullOrEmpty(context.Request.Headers["If-Modified-Since"]))
            {
                DateTime IfModifiedSince = DateTime.Parse(context.Request.Headers["If-Modified-Since"]);
                if (IfModifiedSince > Now)
                {
                    context.Response.StatusCode = 304;
                    return;
                }
            }
            //你可以在这里获取图片的ID，然后判断是否属于用户的，是才输出，不是输入默认图片
            //string folder = context.Request.QueryString["Folder"];
            string filepath = context.Request.QueryString["FilePath"];
            int width = int.Parse(context.Request.QueryString["Width"]);
            int height = int.Parse(context.Request.QueryString["Height"]);
            string hex = context.Request.QueryString["Hex"];            string path = context.Server.MapPath(string.Format("/QshopImg/{0}", filepath));            byte[] bytes = ImageHelper.Reset(path, width, height);
            //System.Drawing.Image img = ImageHelper.Reset(bytes, width, height);            context.Response.Headers["Last-Modified"] = Refresh.ToString();
            //context.Response.Cache.SetExpires(DateTime.Now.Add(Refresh));
            //context.Response.Cache.SetMaxAge(refresh);
            context.Response.Cache.SetCacheability(HttpCacheability.Public);
            context.Response.CacheControl = HttpCacheability.Public.ToString();
            context.Response.Cache.SetValidUntilExpires(true);
            //context.Response.StatusCode = 304;
            //img.Save(context.Response.OutputStream, ImageHelper.GetImageFormat(path));
            context.Response.ContentType = "image/" + hex;
            
            context.Response.BinaryWrite(bytes);        }        public bool IsReusable
        {
            get
            {
                return false;
            }
        }
    }