for(var i=0; i<document.images.length; i++) {
  if (document.images[i].name.indexOf("swap_") == 0) {
    eval(document.images[i].name + "_c = new Image()");
    eval(document.images[i].name + "_n = new Image()");
    var thenormsrc = document.images[i].src;
    var fileext = thenormsrc.substring(thenormsrc.length-4);
    eval(document.images[i].name + "_c.src = '" + thenormsrc.substring(0,thenormsrc.length-6) + "_m" + fileext + "'");
    eval(document.images[i].name + "_n.src = '" + thenormsrc + "'");
  }
}
function swapImage(img) {
  document.images[img].src = eval(img + '_c.src');
}
function reSwapImage(img) {
  document.images[img].src = eval(img + '_n.src');
}