im1 = new Image();
im2 = new Image();
im3 = new Image();
im4 = new Image();

im1.src = "img/entree_b.gif";
im2.src = "img/sortir_b.gif";
im3.src = "img/entree.gif";
im4.src = "img/sortir.gif";

function changeImage(nomIm,src)
{
  document.images[nomIm].src = src;
}