* List untagged images? 

* Allow queries, e.g. tag conjunction, disjunction and negation,
  images without tags, etc.

* Show uploaded images after upload.

* Selectable image sorting.

* Allow limiting number of thumbnails per page.

* Fix the goto next page feature implementation.
  It seems very fragile.

* Stay on the same page when switching to/from admin mode.

* Allow flexible thumbnail box heights.

* AJAX add tag.

* Changing (deleting, adding tags) multiple images.

* Rotate image using EXIF info.

* Allow tagging tags?

* Authentication?

* Use more efficient representation of contents of uploaded files.