jquery.naturalWidth.js

// jQuery.naturalWidth / jQuery.naturalHeight plugin for (already-loaded) images

// Triple-licensed: Public Domain, MIT and WTFPL license - share and enjoy!

(function($) {
  function img(url) {
    var i = new Image;
    i.src = url;
    return i;
  }

  if ('naturalWidth' in (new Image)) {
    $.fn.naturalWidth  = function() { return this[0].naturalWidth; };
    $.fn.naturalHeight = function() { return this[0].naturalHeight; };
    return;
  }
  $.fn.naturalWidth  = function() { return img(this[0].src).width; };
  $.fn.naturalHeight = function() { return img(this[0].src).height; };
})(jQuery);

Added a fix to the original in order to make this work in Internet Explorer 8... :)

nice...