pgGallery is the opened sourcing of my personal photo gallery development effort. I started in mid-2010 and open sourced in November of 2010. Currently the source code is hosted on github.
I think the most important guiding direction for a new project is to define what something is and more importantly what something is NOT. pgGallery is designed to be a web based photo gallery for the management of up to 100,000 photos and videos. It is not intended to be a flickr or other large scale image hosting solution. The ideal use case for this application is a family archivist, who has to manage a large number of probably unorganized photos and allow limited access to them.