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.

Bjørn Johansen

This is a WordPressified version of the excellent, lightweight (for real!) imageLightbox.js (MIT-licensed) by Osvaldas Valutis (http://osvaldas.info/image-lightbox-responsive-touch-friendly)
This is his introduction to the lightbox: 
“As for the image lightboxes, I have always lacked simplicity for them. I mean not only the visual design, but the overall experience: from implementation to UX. All due respect, but I have never liked any of these light-fancy-face-boxes. They all were solving problems that just don’t exist: lots of unwanted features by default, total mess in markup, no native behavior for touch screens. I was working on a project and needed an image lightbox that solves these problems. I needed a lightbox only for images, not video, text, and iframes at once. I made ImageLightbox.js.”
This version autodetects all links to image files and opens them in the lightbox.
For your “install, activate and go”-convenience, this plugin comes with a minimal CSS that easily can be deactivated and/or replaced.
The plugin can also be themed to your liking. An example theme is available here: https://github.com/bjornjohansen/imagelightbox-theme-smooth
Please let me know if you have any issues. Fastest way to get a response is by Twitter: https://twitter.com/bjornjohansen

imageLightbox

Image Lightbox, Responsive and Touch‑friendly.

jQuery Lightbox For Native Galleries vs imageLightbox