function openImage(imageName,alt) {
  width=500;
  height=500;
  posX=(screen.availWidth-width)/2;
  posY=(screen.availHeight-height)/2;
  popImage=window.open(imageName,'','width='+width+',height='+height+',left='+posX+',top='+posY+',resizable=1,scrollbars=1');
}