Saw this linked in a WordPress support forum post. May bear some investigation.

Relatively Absolute: Simple PHP Gallery

Features

Simple PHP Gallery is a gallery management system designed to tackle small- to medium-size galleries with a minimum of hassle. While SPG sacrifices a few of the bells and whistles of other gallery systems in favor of simplicity, ease-of-use, and speed, it boasts a large feature set:
Version 1.1
Screenshot of Simple PHP Gallery 1.1

All of the features of 1.0, plus:

* Significant speed enhancements.
* Image precaching – significantly improves the appearance of speed when paging through images.
* Better compatibility with GD 1.x
* Better quality generated images with GD 2.x functions.
* Image resizing – Bypass your photo editing software and resize your images on the fly!
* Image caching – SPG 1.1 can resize your images once, then save the generated files forever!
* Accesskey navigation – Alt [-] for the previous image, Alt [ ] for the next image, Alt [u] to move up one level. (In accesskey enabled browsers)
* Compatible out-of-the-box with Dan Benjamin’s Better Image Rotator.
* Aliases and descriptions for images and folders, controled via an easy-to-edit ini file.
* Automatically generated sub-folder details.
* Automatic thumbnail alignment.
* Folder hiding – keep that pesky ‘cgi-bin’ folder from showing up in your gallery.
* Improved sorting – folder lists are now sorted alphabetically by alias or file name.
* Myriad bug fixes and improved all-around compatibility

This may be the first project that I’ve seen use a Creative Commons license for the source code (versus GPL, BSD, MIT, Apache, etc…)