threshold

This script generates a poster like the famous one from Jim Fitzpatrick.
Copy it into the scripts folder from GIMP, you will find it then under Filters -> Artistic -> Che Guevara.
See also the Obama "HOPE" Script.
Example here:

To fix burned out or white skies by adding clouds and a blue sky gradient (using a threshold mask).

Guide to Using the Blue Sky & Clouds Script

To fix burned out or white skies by adding a blue sky gradient (using a threshold mask).

Guide to Using the Blue Sky Gradient Script

Adds a Contrast Adjustment layer to your image to help fix contrast problems.

Guide to Using the Contrast Fix Script