jQuery.fn.retina = function(retina_part) {
    // Set default retina file part to '-2x'
    // Eg. some_image.jpg will become some_image-2x.jpg
    var settings = {'retina_part': '-2x'};
    if(retina_part) jQuery.extend(config, settings);

    if(window.devicePixelRatio >= 2) {
        this.each(function(index, element) {
            if(!$(element).attr('src')) return;

            var new_image_src = $(element).attr('src').replace(/(.+)(\.\w{3,4})$/, "$1"+ settings['retina_part'] +"$2");
            $.ajax({url: new_image_src, type: "HEAD", success: function() {
                $(element).attr('src', new_image_src);
            }});
        });
    }
    return this;
}