public function add_image_sizes_meta_to_media($form_meta, $post = null)
    {
        if (wp_attachment_is_image($post->ID) && current_user_can('manage_options')) {
            $meta = wp_get_attachment_metadata($post->ID);

            $form_meta .= '<strong>Available sizes: </strong>' . \count($meta['sizes']);
        }

        return $form_meta;
    }