Alex Mills

DISCONTINUATION NOTICE: Development on this plugin has ceased in favor of the carousel module in the <a href="https://wordpress.org/extend/plugins/jetpack/" rel="ugc">Jetpack plugin</a>. I recommend you use that plugin instead — it’s much more full featured.
Makes the native WordPress galleries use a lightbox script called <a href="http://colorpowered.com/colorbox/" rel="nofollow ugc">ColorBox</a> to display the fullsize images right there in the page. No modifications required.
You can also make single non-<code>[gallery]</code> images use the lightbox by giving their links a class of “lightbox”, like so:
<pre><code><a href="..." class="lightbox"><img src="..." alt="..." /></a>
</code></pre>

jQuery Lightbox For Native Galleries

Makes the native WordPress galleries use a lightbox script called ColorBox to display the fullsize images.

omerk

<a href="http://fancybox.net/" rel="nofollow ugc">Fancybox</a> is a tool for displaying images, html content and multi-media 
in a Mac-style “lightbox” that floats overtop of web page. It was built using the jQuery library.
This plugin inserts the necessary elements required to run Fancybox on your blog. It also groups 
images within posts using rel attributes. (Based on the code found on <a href="https://wordpress.org/support/topic/automatic-adding-lightbox-rel-and-group-to-images-in-posts" rel="ugc">this</a> 
forum thread)
To disable Fancybox per post: Add a custom field called ‘nofancybox’ and set it’s value to ‘true’. 
Instructions on how to add custom fields to posts can be found at <a href="https://codex.wordpress.org/Custom_Fields" rel="nofollow ugc">this</a> 
codex article.

Fancyboxify

This simple plugin enables Fancybox on image links. It groups all images within a single post and can also be disabled per post.

jQuery Lightbox For Native Galleries vs Fancyboxify