gistfile1.txt

document.observe("dom:ready", function()
{
  var images = $$('img'); // img should replaced with a selector, like img.thumbnail
  images.each( function(img)
  {
    Event.observe(img, 'mouseover', function()
    {
      console.log("yarrr");
      $('my-image-placeholder').setAttribute('src', 'the-image-location.png');
    });
  });
});