One of the reasons why Justified Image Grid has a model that lacks its own content source is the ease of use of external sources. Most people are already familiar with uploading pictures to Facebook. This allows to leverage the fact that no technical skills are required to manage and maintain galleries over time. Once you connect the plugin to Facebook, just keep adding photos. However, you will not only build Zuck's site, but also your own! How? Your Facebook albums can simply appear in WordPress using Justified Image Grid.
If you are a developer, why would you care?
Less work for you! Wouldn't it be cool to tell your client that he or she can just manage the site's photos from Facebook? They'll be delighted to know that there is nothing new to learn. You just set up one gallery for them and everytime they add new stuff, it'll get synced to their website. Not just in any way but as a beautiful justified grid. Various built-in modes help to show multiple or single albums in the most useful ways. The point is to set it and forget it, for a self-updating section on the site which is sourced from a Facebook profile or page. Read on to learn how this works!
Learn more about what can you display from Facebook!
Each display mode has more detailed demos and explanations to find out which one suits you best. This is an index page for the Facebook source.