//get all images inside entry content
jQuery(document).ready(function(){
    jQuery(".entry-content img").each(function(){
//get the URL of the image
        var the_url = jQuery(this).attr('src');
//insert a href before image where rel=lightbox
        var a = jQuery("<a></a>").attr({"href": the_url, "rel": "lightbox"});
        jQuery(this).wrap(a);
        jQuery(this).load(function(){
            var the_width = jQuery(this).width();
            var the_height = jQuery(this).height();
            var max_dimension = 600;
            if (the_width && the_height){
                var ratio = the_width / the_height;
                if (ratio >= 1 && the_width > max_dimension){
                    jQuery(this).css('width', max_dimension);
                    jQuery(this).css('height', the_height * max_dimension / the_width);
                }
                else if (ratio > 1 && the_height > max_dimension){
                    jQuery(this).css('height', max_dimension);
                    jQuery(this).css('width', the_width * max_dimension / the_height);
                }
            }
        });
    });
});