add gallery image caption

<script>
(function($) {
    $(document).ready(function() {
        var galleryItem = $('.custom-gallery .et_pb_gallery_item .et_pb_gallery_image');
        galleryItem.each(function(){
            var img = $(this).find('img'),
                caption = img.attr('alt');
            $('<p class="wpc-caption">'+caption+'</p>').insertAfter(img);
        })
    });
})(jQuery);
</script>