Vergilius

Actually, I solved the problem. My solution:

$photocount=$wpdb->get_var($wpdb->prepare(“SELECT COUNT(*) FROM $wpdb->posts WHERE post_type = ‘attachment’ AND post_parent IN (SELECT ID FROM $wpdb->posts WHERE post_type = ‘my_posttype’)”));
echo $photocount;

Temporary i’m using javascript:

$(document).ready(function() {
    $(".gallery a").addClass("photo");
    $(".gallery a").each(function() {
      this.rel += 'gal';
    });
});

This snippet adds class=”photo” and rel=”gal” for all links inside gallery div.