Add Copyright-information to lightbox title

Hi,

I want to add the copyright information (_avia_attachment_copyright) underneath the lightbox.

Already found out that I can access the copyright information for attachments with following code in php-files:
get_post_meta($attachment_entry->ID, '_avia_attachment_copyright', true )

I also found out that I have to edit the function according titleSrc in the file avia-snippet-lightbox.js to change the title underneath the lightbox.

But I don’t know how to access the copyright-information in javascript.
Maybe someone could help me.

Thanks
Niklas