Social Gallery is the Ultimate Social Lightbox Plugin for WordPress. This is the Lite Version.
For some reason the most essential instruction is the hardest to find in the install guides and help forum. For any image you wish to use as the lightbox, you must change the Link CSS Class to socialGallery. Then it works like a charm. You can find an input box in your Image Detail popup to enter socialGallery, or you can change the code as follows (simplified to just the essential required code):
<a class="socialGallery" href="Full Size Image URL"><img src="Thumbnail or Custom Size Image URL"></a>
I loved the idea of this plugin when I saw it on some website. After implementing on my site I found it is not responsive for mobile versions. Only an addon is available which is really not the best way to go, the least they could offer is to disable the gallery on mobile phones option. More than 50% viewers these days are from mobile, so I had to take it down.