img1 = new Image();  img1.src = "images/a0.jpg";
  img1h = new Image(); img1h.src = "images/a1.jpg";
  img2 = new Image();  img2.src = "images/b0.jpg";
  img2h = new Image(); img2h.src = "images/b1.jpg";
  img3 = new Image();  img3.src = "images/c0.jpg";
  img3h = new Image(); img3h.src = "images/c1.jpg";
  img4 = new Image();  img4.src = "images/d0.jpg";
  img4h = new Image(); img4h.src = "images/d1.jpg";
  img5 = new Image();  img5.src = "images/e0.jpg";
  img5h = new Image(); img5h.src = "images/e1.jpg";
  img6 = new Image();  img6.src = "images/f0.jpg";
  img6h = new Image(); img6h.src = "images/f1.jpg";

function swap(x,img_obj)
{
    x.background = img_obj.src;
}