gistfile1.js

var images = $('photoBox').hide().select('img');
images.each(function(img){
  var link = new Element('a');
  $('pickerBox').insert(link.wrap('p'));
  link.href = img.src;
  link.update(img.alt);
});
$('pickerBox').observe('click', function(evt){
  var elm;
  if(elm = evt.findElement('a')){
    evt.stop();
    document.body.background = elm.href;
  }
});
document.body.background = images.first().src;