This page contains a simple plugin for the GIMP that allows you to open an Octave prompt inside the GIMP to edit the current image.
The following image shows how things look
To download the plugin, click here
To install the plugin, just untar the file and run 'make'. You need the gimp developer tools plus 'vte' for this.
To use the plugin open an image in the GIMP, and go to 'Filters' -> 'Mathematics' -> 'Octave Terminal'.