>>106125631Wouldn't work if they already had you as a suspect and knew your printer's serial number. You'd just have to overlay the true dot pattern onto the printed document and you'd clearly see that 100% of the overlaid dots line up with the printed document, even if there is random noise.
Also probably wouldn't in general, since a sufficiently good statistician could probably identify which dots are random and which form a pattern and with the appropriate statistical moments to match the types of pattern used for the secret dots.
>>106119008The absence of evidence that they've found a monochrome solution isn't evidence of absence. For all you know, they could be printing micro-dots much smaller than normal print resolution. Or printing negative-dots within the actual printed content (i.e. microscopic gaps inside letters). Or maybe they've etched the dots into one of the roller drums inside the printer and it embosses the paper as it rolls through, and if you shine laser light at the correct angle the dots become visible. Or maybe they don't even need to modify the rollers, because there's enough random variation in the machinery of the printer that affects the printed output that you can identify printers with 95% accuracy and that's good enough for "beyond a reasonable doubt."
>>106125650Thermal printer would be easier. Laser is overkill for sure, just need a thermal resistor. Might don't even need a moving head, if you created (or purchased) a dot-matrix style array of heating elements and just pulsed them as the paper rolls through.