if (document.images) 
{
   img1 = new Image();
   img2 = new Image();
   img3 = new Image();
   img4 = new Image();
   img5 = new Image();
   img6 = new Image();
   img1.src = "images/pic-dandelion.jpg";
   img2.src = "images/pic-trees.jpg";
   img3.src = "images/pic-starfish.jpg";
   img4.src = "images/pic-lake.jpg";
   img5.src = "images/pic-forest.jpg";
   img6.src = "images/pic-autumn.jpg"
}