var nb_photos_vert = 20;  // _vert0.jpg à _vert19.jpg

var arrPhotos            = new Array ();

var precedIndex=0;
var timer_img_aleatoire;

function diplay_img_aleatoire(){

   indexPhoto1 = Math.floor(Math.random()*arrPhotos.length);

   if(indexPhoto1!=precedIndex){
      precedIndex = indexPhoto1;
      document.images['img1'].src = arrPhotos[indexPhoto1];

      var indexPhoto2 = Math.floor(Math.random()*arrPhotos.length);
      if(indexPhoto2!=indexPhoto1){
          document.images['img2'].src = arrPhotos[indexPhoto2];
      }
   }

}

function start_img_aleatoire(){
   timer_img_aleatoire = window.setInterval("diplay_img_aleatoire()", 7000);
   for(var i=0; i<nb_photos_vert;i++){
     arrPhotos[i]= "photos/_vert" + i + ".jpg";
   }
}