GIMP Plugin Registry

Script to randomly mix cells of a selection. The bounding box of the current selection will be used automatically to eliminate non-rectangular and feathered selection. After specifying the count of columns and rows in the selected region the width and height of the selection will be reduced if necessary (thus ensured the divisibility of the selection). The script will then shuffle the cells inside the selection and return the mixed image on a new layer or in place of the original layer.

This script creates small rectangular selections and auto-white-balances them.
Copy it into the scripts folder from GIMP, you will find it then under Filters -> Light and Shadow -> White Balance Puzzle.  read more »