(function($) {

    $.fn.lazyload = function(options) {
        var settings = {
            threshold : 0
        };

        if(options) {
            $.extend(settings, options);
        };

        var elements = this;
        if (!settings.event) {
            $(window).bind("scroll", function(event) {
                elements.each(function() {
                    if (!this.loaded && !$.belowthefold(this, settings)
                                     && !$.rightoffold(this, settings)) {
                                         $(this).attr("src", $(this).attr("original"));
                                         this.loaded = true;
                    };
                });
                var temp = $.grep(elements, function(element) {
                    return !element.loaded;
                });
                elements = $(temp);
            });
        };

        return this.each(function() {
            var self = this;

            $(self).attr("original", $(self).attr("src"));
            if (settings.event || $.belowthefold(self, settings)
                               || $.rightoffold(self, settings)) {
                if (settings.placeholder) {
                    $(self).attr("src", settings.placeholder);
                } else {
                    $(self).removeAttr("src");
                }
                self.loaded = false;
            } else {
                self.loaded = true;
            }

            if (settings.event) {
                $(self)[settings.event](function(event) {
                    if (!self.loaded) {
                        $(self).attr("src", $(self).attr("original"));
                        self.loaded = true;
                    };
                });
            };
        });

    };

    $.belowthefold = function(element, settings) {
        var fold = $(window).height() + $(window).scrollTop();
        return fold <= $(element).offset().top - settings.threshold;
    };

    $.rightoffold = function(element, settings) {
        var fold = $(window).width() + $(window).scrollLeft();
        return fold <= $(element).offset().left - settings.threshold;
    };

    $.extend($.expr[':'], {
        belowthefold : "$.belowthefold(a, {threshold : 0})",
        abovethefold : "!$.belowthefold(a, {threshold : 0})",
        rightoffold  : "$.rightoffold(a, {threshold : 0})",
        leftoffold   : "!$.rightoffold(a, {threshold : 0})"
    });

})(jQuery);