[Printers] obfuscate dots?

[Ringo Kamens]

If you took the color cartridge out and printed in B+W would it remove
the dots? Do you know of any old color printers that don't have this
feature that you can still buy ink for? If the ink is the same as the
yellow color ink, then a light chemical wash might be able to remove
the dots but not enough of the regular yellow ink to make a noticeable
difference.
Just some thoughts
Comrade Ringo Kamens

On 4/15/07, Seth David Schoen <schoen at eff.org> wrote:
> Ringo Kamens writes:
>
> > Unfortunately it wouldn't work. To the naked eye it would work but I
> > think that forensics would be able to tell that they were made
> > differently. Wouldn't it just be better to completely remove/cover the
> > device that puts the yellow dots in? I also had similar questions and
> > would appreciate a response from somebody more in the know.
>
> My current opinion is that the dots are produced by the same mechanism
> as regular printer output; that is, they are added by software inside
> the printer rather than produced by separate imaging hardware.
>
> If they are pixel-sized and pixel-aligned, and always appear in the
> same offset to the edges of the paper, it should be possible to produce
> some kind of obfuscating overlay.  I know that I've argued in the
> past that this was impossible, but I now think it would be possible
> if the printer dots produced by a particular printer model are really
> made of ordinary yellow pixels and if their offset to the edges of the
> page isn't randomized.
>
> Actually getting this right is a little bit tricky, but I've recently
> experimented with printing 1x1, 2x2, and 3x3 pure yellow squares at
> fixed locations on an HP Color LaserJET and then looking at them under
> a microscope to compare with the tracking dots the CLJ is adding.  The
> results are promising but not at all definitive; one thing that would
> help is a much better microscope to try to clear up the question of
> whether the tracking dots are distinguishable under much greater
> magnification.)
>
> I'll try to give an update about this soon; I'm going to be speaking
> about printer dots at the meeting of the National Association of Document
> Examiners next month and I'm hoping to be able to tell them more about
> whether this countermeasure would actually work.
>
> --
> Seth Schoen
> Staff Technologist                                schoen at eff.org
> Electronic Frontier Foundation                    http://www.eff.org/
> 454 Shotwell Street, San Francisco, CA  94110     1 415 436 9333 x107
>