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Xerox Photocopiers Randomly Alter Numbers, Says German Researcher
First time accepted submitter sal_park writes "According to a report from German computer scientist D. Kriesel, some Xerox WorkCentre copiers and scanners may alter numbers that appear in scanned documents. Having analyzed the output of two such devices, the Xerox WorkCentre 7535 and 7556, Kriesel found that "patches of the pixel data are randomly replaced in a very subtle and dangerous way": in particular, some numbers appearing in a document may be replaced by other numbers when it is scanned."
The things you learn. I never knew before about JBIG2 and how scanners use it to repeat pieces of image. Seems to me that the JBIG2 parameters are tuned incorrectly in these scanners.
While it isn't nefarious so far as a deliberate plot to destroy documents and their integrity, it is a bug that is of concern for those who want to preserve documents for long-term storage in an archival situation.... such as was the case with the architectural documents being scanned.
Keep in mind that in some archival situations, the original paper documents are destroyed where the scanned versions in these files are all that remains of those documents. Ultimately, by having the numbers change like this, regardless of why it is happening, now throws serious doubt as to the validity of any of the numbers in that document. This can have an enormous set of consequences if you are using this scanned document as a receipt, for banking purposes (aka the check amount might have a different number than was originally used) or other similar kinds of situations. Engineering offices, banks, and a great many other businesses are shredding mountains of paper and archiving those documents electronically, so it is a big deal.
I guess it really boils down to understanding the limitations of compression algorithms, and not buy into the hype that a vendor might have where you can save all kinds of storage space with this incredible algorithm.... and find out that all of your documents are worthless when you try to submit them to a judge & jury in a lawsuit as evidence. Perhaps an engineer needs to find the dimensions and tolerance limits of a bolt in an obscure subsystem... and the numbers change? Do you really want to fly in an airplane where the parts specifications have changed because of an error like this? Do you mind if a few hundred or even thousand dollars are taken out of your bank account that you didn't authorize?
Ran some numbers to check, and with some assumptions your estimate seems pretty close.
The modern standard "postscript point" is 1/72 in, so a 7-point font has a height 7/72 inches. The stroke distinguishing the 6 from the 8 is maybe 1/4 of the height, so let's say ~0.025 inches. If the print/scan cycle roundtrips at somewhere in the range 75-150 dpi, that's 2-4 pixels. If you can manage a professional-standard 300 dpi, you get more like 7-8 pixels, but that's a fairly optimistic case.
Why wouldn't you use at least 300dpi?
Most "serious" office printers print at 600dpi or better, so the information is there. Even my $100 brother laser printer defaults to 600dpi. Every recent office multifuntion I have seen can scan at 200, 300, or 600dpi, but every single one defaults to 200dpi. 200dpi scans are hard on the eyes. I always scan at 600dpi, the file size isn't bad in the age of 300GB laptop hard drives, and if I need to send it to someone external to the company, I can always reduce the size.
Even those who arrange and design shrubberies are under considerable economic stress at this period in history.
So you're telling us this is a problem caused by a user not RTFMing and Slashdot sensationalized it?
Surely you're joking. :P
I admit that I, for one, don't usually RTFM before using the copier. Certainly not when I'm using the copier in "Normal" mode.
And don't call me "Shirley".
I am not a crackpot.
It could just be a particularly poor JBIG implementation: the format and decompressor is standardized, but the standard doesn't specify how to find the matches, so various companies have their own proprietary versions.
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
This is how people get shot, because the police are given the wrong address to raid a house. This is how people get foreclosed on because a few account numbers are switched.
Holy crap. That makes me never want to go near a copier again.
If telephones are outlawed, then only outlaws will have telephones.