Find & remove white framing from stereophoto maker paired images

This script finds and removes the white framing around and inside stereo pair images assembled with stereophoto maker with the default settings. (Tested and running with Gimp 2.4.5)

see also:
http://registry.gimp.org/node/8617, script to bisects a stereo image into two layers,
http://registry.gimp.org/node/10170, script to adjoin two separated stereo layers