//例項化WebRequest物件   

 WebRequest wreq = WebRequest.Create(url);// url圖片地址

 //建立HttpWebResponse物件

HttpWebResponse wresp = (HttpWebResponse)wreq.GetResponse();

//建立流物件

Stream s = wresp.GetResponseStream();

System.Drawing.Image img;

 img = System.Drawing.Image.FromStream(s);               

  img.Save(Server.MapPath("儲存路徑") +"儲存得圖片名稱", ImageFormat.Png);// ImageFormat.Png為圖片格式