function imgOn(imgName, imgFile, alt) {
   if (document.images) {
      document[imgName].src = imgFile;
	  //document[imgName].alt = alt;
   }
}

function imgOff(imgName, imgFile, alt) {
   if (document.images) {
      document[imgName].src = imgFile;
	  //document[imgName].alt = alt;
   }
}