function viewPicture(picture, width, height, topmargin)
{
  var overlay = document.getElementById('overlay');
  overlay.style.margin = topmargin+"px auto";
  overlay.style.visibility = "visible";
  var overlaid = document.getElementById('overlaid');
  overlaid.style.width = width+"px";
  overlaid.style.height = (height+15)+"px";
  var overlayimg = document.getElementById('overlayimg');
  overlayimg.src = picture;
}