// create our transition as a plugin
$.fn.crossfade = function () {
  return this.each(function () { 
    // cache the copy of jQuery(this) - the start image
    var $$ = $(this);
    
    var target = $$.attr("src").replace(/.png$/ig, "_on.png");
    
  // nice long chain: wrap img element in span
                $$.wrap('<span style="position: relative;"></span>')
                    // change selector to parent - i.e. newly created span
                    .parent()
                    // prepend a new image inside the span
                    .prepend('<img>')
                    // change the selector to the newly created image
                    .find(':first-child')
                    // set the image to the target
                    .attr('src', target);

                // the CSS styling of the start image needs to be handled
                // differently for different browsers
                if ($.browser.msie || $.browser.mozilla) {
                    $$.css({
                        'position' : 'absolute', 
                        'left' : 0,
                        'background' : '',
                        'top' : this.offsetTop
                    });
                } else if ($.browser.opera && $.browser.version < 9.5) {
                    // Browser sniffing is bad - however opera < 9.5 has a render bug 
                    // so this is required to get around it we can't apply the 'top' : 0 
                    // separately because Mozilla strips the style set originally somehow...                    
                    $$.css({
                        'position' : 'absolute', 
                        'left' : 0,
                        'background' : '',
                        'top' : "0"
                    });
                } else { // Safari
                    $$.css({
                        'position' : 'absolute', 
                        'left' : 0,
                        'background' : ''
                    });
                }
 
    // similar effect as single image technique, except using .animate 
    // which will handle the fading up from the right opacity for us
    $$.hover(function () {
      $$.stop().animate({
          opacity: 0
      }, 250);
    }, function () {
      $$.stop().animate({
          opacity: 1
      }, 1000);
    });
  });
};

// Not only when the DOM is ready, but when the images have finished loading,
// important, but subtle difference to $(document).ready();
$(window).bind('load', function () {
  // run the cross fade plugin against selector
  $('img.fade').crossfade();
});