This addon requires List Files from Set to be installed first.  

Add a List Files from Set block to list files from a fileset containing images.

Save the block and select one of the thumbnails_with_links templates.

Advanced Stuff

The DOM output is compatible with fancybox, so a developer can easily add a small snippet of jQuery to turn this into a popup image gallery, perhaps using an addon such as jQuickie to do so.

The DOM output is also compatile with Front End List Magic for front end manipulation and pagination of the thumbnail list.

Combine all this with a Front End File Uploader block and you have a gallery that can be managed from the front end with minimal end-user expertise.