This isn’t new (from 2005), but I ran across it today and found it interesting. These dots can be used by law endorsement to tell what printer printed something and when. It’s designed to find counterfeiters, but I bet it will show up in trials for other things, too.

EFF: DocuColor Tracking Dot Decoding Guide

This guide is part of the Machine Identification Code Technology project. It explains how to read the date, time, and printer serial number from forensic tracking codes in a Xerox DocuColor color laser printout. This information is the result of research by Robert Lee, Seth Schoen, Patrick Murphy, Joel Alwen, and Andrew “bunnie” Huang. We acknowledge the assistance of EFF supporters who have contributed sample printouts to give us material to study. We are still looking for help in this research; we are asking the public to submit test sheets or join the printers mailing list to participate in our reverse engineering efforts.

The DocuColor series prints a rectangular grid of 15 by 8 miniscule yellow dots on every color page. The same grid is printed repeatedly over the entire page, but the repetitions of the grid are offset slightly from one another so that each grid is separated from the others. The grid is printed parallel to the edges of the page, and the offset of the grid from the edges of the page seems to vary. These dots encode up to 14 7-bit bytes of tracking information, plus row and column parity for error correction. Typically, about four of these bytes were unused (depending on printer model), giving 10 bytes of useful data. Below, we explain how to extract serial number, date, and time from these dots. Following the explanation, we implement the decoding process in an interactive computer program.

Here’s an article from 2005 about the research.