This is a modified version of the script at http://registry.gimp.org/node/22018 which allows you to run it from the command line, automatically merging the layers and saving to the same filename. I also created a simple batch wrapper around this, based on the code at http://www.gimp.org/tutorials/Basic_Batch/ and sliced and diced it appropriately.
[Taken from the original script page, hope they don't mind!]
The script makes a pencil drawing from a photo. It's very easy to handle.
The original tutorial can be found here: http://www.gimpusers.com/tutorials/making-a-pencil-drawing-from-a-photo....
Here you can see a little example:
The G'MIC plug-in for GIMP proposes a set of various filters to apply on your images, including artistic effects, image denoising and enhancement algorithms, 3D renderers, etc.. It is a quite large plug-in, integrating a lot of different effects.
Script to create pencil drawing from photographic image. Based on the Tutorial:
Making a pencil drawing from a photo, written by devv: (www gimpusers com/users/devvv.html)
Unless otherwise noted, the rights for the individual plugins are with their respective authors. Logo image by Jakub Steiner.