function emptyField(id) {
   var titulok = document.getElementById(id);
   titulok.value = "";
}

    if (document.images)
    {
      preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "http://www.aircraftgallery.eu/images/logos/logo_1_bw.png";
      image_url[1] = "http://www.aircraftgallery.eu/images/logos/logo_2_bw.png";
      image_url[2] = "http://www.aircraftgallery.eu/images/logos/logo_3_bw.png";
      image_url[3] = "http://www.aircraftgallery.eu/images/logos/logo_4_bw.png";
      image_url[4] = "http://www.aircraftgallery.eu/images/logos/logo_5_bw.png";
      image_url[5] = "http://www.aircraftgallery.eu/images/logos/logo_6_bw.png";
      image_url[6] = "http://www.aircraftgallery.eu/images/logos/logo_7_bw.png";
      image_url[7] = "http://www.aircraftgallery.eu/images/logos/logo_8_bw.png";
      image_url[8] = "http://www.aircraftgallery.eu/images/logos/logo_9_bw.png";
      image_url[9] = "http://www.aircraftgallery.eu/images/logos/logo_10_bw.png";
      image_url[10] = "http://www.aircraftgallery.eu/images/logos/logo_11_bw.png";
      image_url[11] = "http://www.aircraftgallery.eu/images/logos/logo_12_bw.png";
      image_url[12] = "http://www.aircraftgallery.eu/images/logos/logo_13_bw.png";
      image_url[13] = "http://www.aircraftgallery.eu/images/logos/logo_14_bw.png";
      image_url[14] = "http://www.aircraftgallery.eu/images/layout/default/submit_search_bw.png";

       var i = 0;
       for(i=0; i<=14; i++)
         preload_image_object.src = image_url[i];
    }