get image meta data from gallery in functions.php

Hi,

I’am building my page on WordPress 3.7.1 and I have problem with getting meta data (image title and description). I would like hook lightbox (jackbox) to my gallery so i must change some code in default gallery becouse. I must add to class=”jackbox” data-title=”$image title” and data-description=”$image_description”. I found function to add class=”jackbox”

function my_get_attachment_link($html) {
$postid = get_the_ID();
$html = str_replace('<a', '<a class="jackbox" data-group="info" data-title="'.$img_title.'"', $html);
return $html;
} add_filter('wp_get_attachment_link', 'my_get_attachment_link', 10, 1);

when i add class=”jackbox” i tried add data-title=”$img_title” but i cant generate image meta data.

Best Regards
Michal