Super simple cheezy image gallery that makes its own thumbnails. I worked this up quick-like for a simple site I was working on. Check out the index.php file as an example of how to use it. Should be easy to modify to your liking. Just stick each gallery's images in its own subdirectory of some directory.
When cheezy_gallery.php is executed, a couple globals are set from the query-string, if found there. $directory is the directory/gallery selected and $feature is the filename of the image to feature big-like at the top.
gallery() displays a table of the images in the given directory, with the "feature" image at the top (or not). list_galleries() spits out a list of links for each folder of images.
Since thumbnails are generated as-needed, if you upload a grip of images the gallery will probably be really slow first time you go to it and you might even have to refresh a couple times. After that though, assuming you add just a few new files at a time, probably won't be a problem.
License: WTFPL http://www.wtfpl.net/txt/copying/