Pictag is a simple web photo gallery with automatic thumbnail generation and tagging capability. It's self-contained in a single file, uses the file system for gallery layout, and requires no stand-alone database (it uses SQLite) or no database at all. It handles EXIF data, provides support for HTTP user authentication and authorization, and it's customizable.
For the longest time I've used Apache::Gallery for organizing and viewing my pictures on the web. It was old but it did what I needed. However things change, and I longed for the capability to add descriptions to images, and tag them with specific words like "best" or "better" or "family". I searched around for some replacements and found Single File PHP Gallery (SFPG), which was basically Apache::Gallery in PHP, but had none of the features I really wanted - it was just newer. So I decided to use SFPG as a base to hack in my wish list. It, however, ended up an almost complete rewrite to include some security enhancements, the tagging and description capability using SQLite, image resizing and EXIF interpretation for auto-rotation, and user authentication support. Thus, Pictag was born.