Displaying Image Caption at Functions.php in Wordpress - wordpress

Question

in our wordpress site we modified image gallery style with using theme functions. We changed div classes, ids to use jquery image slider.
To make this we used this codes on functions.php
add_filter('post_gallery', 'ct_post_gallery', 10, 2);
function ct_post_gallery($output, $attr) {
global $post;
if (isset($attr['orderby'])) {
$attr['orderby'] = sanitize_sql_orderby($attr['orderby']);
if (!$attr['orderby'])
unset($attr['orderby']);
}
extract(shortcode_atts(array(
'order' => 'ASC',
'orderby' => 'menu_order ID',
'id' => $post->ID,
'itemtag' => 'dl',
'icontag' => 'dt',
'captiontag' => 'dd',
'columns' => 3,
'size' => 'thumbnail',
'include' => '',
'exclude' => ''
), $attr));
$id = intval($id);
if ('RAND' == $order) $orderby = 'none';
if (!empty($include)) {
$include = preg_replace('/[^0-9,]+/', '', $include);
$_attachments = get_posts(array('include' => $include, 'post_status' => 'inherit', 'post_type' => 'attachment', 'post_mime_type' => 'image', 'order' => $order, 'orderby' => $orderby));
$attachments = array();
foreach ($_attachments as $key => $val) {
$attachments[$val->ID] = $_attachments[$key];
}
}
if (empty($attachments)) return '';
// Here's your actual output, you may customize it to your need
$output = "<div id=\"icmimarlikreferans\">\n";
$output .= "<ul id=\"icmimarlikreferansimg\">\n";
// Now you loop through each attachment
foreach ($attachments as $id => $attachment) {
// Fetch the thumbnail (or full image, it's up to you)
// $img = wp_get_attachment_image_src($id, 'medium');
// $img = wp_get_attachment_image_src($id, 'my-custom-image-size');
$img = wp_get_attachment_image_src($id, 'full');
$output .= "<li class=\"item\">\n";
$output .= "<img src=\"{$img[0]}\" width=\"{$img[1]}\" height=\"{$img[2]}\" alt=\"\" />\n";
$output .= "</li>\n";
}
$output .= "</ul>\n";
$output .= "</div>\n";
return $output;
}
When we use it without making edits WordPress displaying image captions in single post pages at bottom of images in galleries . But when we use this code at functions.php captions are not displaying. We know the caption codes are missing, in this code block what we are using...
We tried to add caption functions in this codes but we have failed.
We need to display image captions at bottom of images in galleries.
We will love you if you help.