[blakecaldwell]

I worked with Keith at the time. Wasn't it true that you guys figured out that the yellow paper had a regular blue dot pattern watermark, and that you were able to use them to help solve that one? If I recall correctly, DARPA didn't know about that.

[otaviogood]

Yes, one of the keys to reconstructing the harder puzzles was that we found a yellow dot pattern on the paper. At the time, I was reading HN and I saw a headline that said something about the government tracking photocopies using little yellow dots. DARPA had photocopied all the docs before shredding them, so they all had a very high-res repeating dot pattern on them. We made our program snap the pieces to the dot pattern. With that in place, the puzzles came together relatively quickly. Some people at DARPA knew about the concept of little yellow dots, but didn't think much of it. I don't blame them. The shredded pieces were so small that it would be hard to imagine any secret pattern helping with the reconstruction. But I guess it helped enough. :)