It’s very simply WordPress plugin for „nice“ shows pictures / galleries in lightbox. This plugin implements javascript library fancybox to header and footer pages created in WordPress, functions:
<ul>
<li>you can configure like original fancybox (in admin menu),</li>
<li>you can use multiple galleries on page,</li>
<li>it’s designed for NextGen Gallery.</li>
</ul>

ZMT fancybox

Plugin adds fancybox code to WP header and footer. This plugin is designed for NextGen Gallery. You can use multiple galleries on page.

Kiran Antony

<h4>Ng Gallery Optimizer Modified</h4>
It is a modified version of <a href="https://wordpress.org/extend/plugins/nextgen-gallery-optimizer/" rel="ugc">Nextgen Gallery optimizer plugin</a> ,which only gives support for “nggallery” shortcode for free.
It improves your site’s page load speed by ensuring NextGEN Gallery’s scripts and styles ONLY load on posts with the nextgen galley shortcode.
It also includes and automatically-integrates the fantastic <a href="http://fancybox.net" rel="nofollow ugc">Fancybox</a> lightbox script, so now you can have gorgeous galleries AND a speedy site! *Requires <a href="https://wordpress.org/extend/plugins/nextgen-gallery" rel="ugc">NextGEN Gallery</a> 1.6.2 and up.
Supports all ten shortcodes of Nextgen Gallery [nggallery id=x], [slideshow id=x], [album id=x], [thumb id=x], [singlepic id=x], [imagebrowser id=x], [nggtags gallery|album=mytag], [random max=x], [recent max=x] and [tagcloud].
It also adds support for the [Show as slideshow] link (loading slideshow scripts only after a user clicks-through)

NG Gallery Optimizer Modified

Improves your site's page load speed by preventing NextGEN's scripts & css from loading on posts and pages without galleries.

ZMT fancybox vs NG Gallery Optimizer Modified