Actually, I am having problem with the wordpress lightbox plugin: Fancybox where it don't work. Therefore, I tried to change to jquery pirobox instead. But I having problem of add the custom rel and class to the link image. I refered http://wordpress.org/support/topic/add-relxyz-to-gallery-link and tried without success moreover I want to add the attribute to certain post only.
Any help or suggestion will be appreciated.

Such a newbie at the time. I will post my debugging result here in case any people having same issue.
The problem is actually missing wp_head()