ePuzzler

I heard about this on NPR. "When the Berlin Wall came down in 1989, East Germany's secret police, the Stasi, frantically tore up millions of files gathered during decades of spying on its own citizens." The Stasi shredded millions of documents. Much of them were shredded using s pecial shredding machines that were able to shred hundreds of meters of files. They shredded so much stuff, the shredders burnt out and the remaining papers had to be ripped by hand. When the stasi finally abandoned their posts and their headquarters were taken over by angry protesters, they left behind 16,000 of those sacks, containing hundreds of millions of pieces of paper. It was estimated it would take decades if not a millennia to put the pieces back together.
This is where computers and algorithms come in. A piece of software was developed with help from the Fraunhofer Society, that uses pattern recognition computer technology to reassemble the pieces together. It's essentially a reverse shredder and they call it the e-Puzzler. You scan torn-up documents into it. It matches up the pieces using color, paper texture, fonts, tear lines and other details. The E-Puzzler machine can process 10,000 two-sided sheets an hour.

Jan Schneider from the Fraunhofer Institute describes the steps as follows:"First we have to digitise all the pieces from the bags. This is done by a special high-speed scanning device.
"The next step is to segment the image itself from the raw scan - we need the outline of the pieces, pixel-wise, to perform the reconstruction process after that.
"Then all digitised pieces of paper are stored in the database. After that we reconstruct a lot of the descriptive features of the pieces."

References:
Stasi files emerge through software
BBC News, Tuesday June 3, 2008
http://news.bbc.co.uk/2/hi/technology/7396272.stm
Piecing Together 'The World's Largest Jigsaw Puzzle'
by Phillip Reeves, NPR News, Monday October 8, 2012
http://www.npr.org/2012/10/08/162369606/piecing-together-the-worlds-largest-jigsaw-puzzle
The machine that is putting together the Stasi's 600m-piece spy jigsaw
Kate Connolly, the Guardian, Wednesday May 9, 2007
http://www.guardian.co.uk/world/2007/may/10/germany.kateconnolly1