Jarkko,
I recommend adding a package_id column to pa_photos. Right now each package maintains the package_id information in the object_type specific table. There has been discussion about moving package_id to acs_objects, but that really won't make your job any easier. Your code is photo-album specific and is free to have knowledge of the photo-album data model.
There also might be other photo-album tables that might need package_id added, I didn't look any further.