function img_unthumb(s) {
  return s.replace(/-thumbnail/, '').replace(/-thumb/, '').replace(/-small/, '');
}

function img_install() {
  var i = 1;
  do {
    var vn = "image" + i;
    var elt = document.getElementById(vn);
    if (!elt) break;

    elt.onclick = function() { 
      document.getElementById('bigimage').src = img_unthumb(this.src);
    }

    if (i == 1) {
      document.getElementById('bigimage').src = elt.src;
    }
  } while (i++ < 1000);
}

if (window.addEventListener) {
  window.addEventListener('DOMContentLoaded', img_install, false);
} else if (window.attachEventListener) {
  window.addEventListener('load', img_install);
} else {
  window.onload = img_install;
}