From: "Robert J. Woodhead" <trebor@foretune.co.jp>
Date: Thu, 21 Oct 93 18:58:04 PDT
To: peb@PROCASE.COM (Paul Baclace)
Subject: Re: Canon copiers
In-Reply-To: <9310212323.AA04196@banff.procase.com>
Message-ID: <9310220156.AA27328@dink.foretune.co.jp>
MIME-Version: 1.0
Content-Type: text/plain


Paul writes:

>I'd like to know how they put the serial number into the copy.

Most likely by modulating the Least Significant Bit of the color
intensity in some (or all) color-filled areas of the image.  A
set of sync-bits, serial number, and some more sync bits.  Repeat
every line, shifted by 1 bit, and you'll get a pattern that is
hard to differentiate from the background unless you _know_
what to look for.

I wouldn't be surprised if there isn't a time and date stamp
as well, plus batch # info.