[PLUG-TALK] Color laser printers and their microdot codes

[Keith Lofstrom]

On Wed, Jun 07, 2017 at 02:19:34PM -0700, Rich Shepard wrote:
>   This is an interesting article on the use of yellow microdots on pages
> printed by color laser printers to record the printer's serial number and,
> often, the date and time the page was printed.
> 
> <http://www.bbc.com/future/story/20170607-why-printers-add-secret-tracking-dots>
> 
>   I use my HP Color LaserJet 2550L (which the EFF documents as printing
> these yellow dots) only for color images such as maps and digital photos. I
> suppose the dots are much more difficult to see on these pages. For plain
> text documents, the HP LaserJet 5 us used to print black text on white
> pages.

First: The dots are imaged with light that makes the yellow
stand out (they look dark in blue light); as long as the
yellow pigment is there, and the whole page is not solid
yellow, the dots can be found.  They are read with high
resolution scanners and software, not a squinty-eyed
clerk with a magnifying glass.  A 8x10.5 imaged area of
a 300 dpi page contains 7.56 million pixels, 30 million
CYMK bits;  you are not expected to "see" a pattern in
30 million bits, but a computer can do so very quickly.

Second: It is also possible to dither black dots on white
paper so that the position changes are unremarkable to the
human eye, but a high-resolution scan reveals much hidden
"watermark" information.  Digimark in Lake Oswego sells
software for such techniques.  

Whinging ON:

Since 98% of the populace is more interested in consuming
than in creating, we passively tolerate the privacy-
destroying "features" of the systems we buy, and the
duopoly political process that mandates them.  Older
machines (with separate Read Only Memory chips) could be
reverse engineered and the ROMs replaced with privacy
enhancing modified code; that would take a few person-
months of skilled work, less if we collaboratively
created tools to automate the process.  

Newer machines require more effort, because the ROMs are
probably built into one complex chip.  Whole boards may
need to be replaced, using less complex chips.  That's why
older machines should be valued and supported by the open
source community; sadly, most open source architects are
feature-chasing consumer junkies as well.  As one who 
values older machines precisely because of this freedom,
I am saddened by this submission to blind consumerism,
and the deteriorating support for the durable used
systems most affordable to the poor.

In 20 years, every single patent in a consumer product has
lapsed; we are free to duplicate those products (with our
own firmware).  That would be a gargantuan effort; we would
need our own chip fabs, and we would need to train teams of
reverse engineers, both in "undeveloped" nations where
labor is cheap and laws are lax.  But we could do so with
a tiny fraction of the effort that goes into new products. 
However, even that relatively small task is unsupportable
with the amount of effort that the few people who claim to
care will actually devote to the problem.  

Fashion or freedom - your choice.

Keith

-- 
Keith Lofstrom          keithl at keithl.com