how to download individual images

I can not write a script that would allow me to download individual images in full quality. I found only this.

<script type="text/javascript">
jQuery().ready(function() {
   jQuery('.ngg-galleryoverview .ngg-gallery-thumbnail a').each(function() {
      var alink = jQuery(this).attr('href');
      jQuery(this).after('<a href="'+alink+'" target="_blank" style="margin:0;">Download</a>')
   });
});
</script>

But then I download it shows when you view thumbnails of all and I want it to in the “Lightbox” which I have set in the gallery via the link: rel = “lightbox [% GALLERY_NAME%].” Can anyone advise me now how do I modify the code, it would probably be best to write it for me? thank you

http://wordpress.org/extend/plugins/nextgen-gallery/