I looked how to customize the template. (nggallery/gallery-dop-thumbnail-gallery.php)
Went in and trid to make some minor changes like hiding the caption over the image, however none of the updates showed up. It just won’t let me customize anything.
This happens because the NextGEN cache. After each change made in the template, save and then go to WP Admin – > Gallery -> Other Options -> Miscellaneous -> Clear image cache , the changes will appear on the site.
Please check: http://andygrosslive.com/museum-collections/