how to clean whiteboard snapshots in general:
  http://matthew.mceachen.us/blog/how-to-clean-up-photos-of-whiteboards-with-gimp-403.html

script for whiteboard cleaning in batch can be found in this folder also.
the batch-whiteboard-clean.scm script should go in: ~/.gimp-2.6/scripts
command:
  gimp -i -b '(batch-whiteboard-clean "*.png")' -b '(gimp-quit 0)'
from site: http://registry.gimp.org/node/19822