This script simulates a photochrom image, a lithographic printing process from the 1890's:http://en.wikipedia.org/wiki/Photochrom
The script is a translation of this how-to for PSE with some improvements:http://www.alibony.com/pse/031508postcard.html
Copy it into the scripts folder from GIMP, you will find it then under Filters -> Artistic -> Photochrom.
Unless otherwise noted, the rights for the individual plugins are with their respective authors. Logo image by Jakub Steiner.