PDA

View Full Version : What's replaced the typewriter identification clue?



tashirosgt
2011-Jan-15, 04:50 PM
Forty years ago, a common development in mystery stories was that a certain document was traced to a particular typewriter. Now that documents are usually printed on laser or inkjet printers, can they be traced to particular machines?

Gillianren
2011-Jan-15, 06:45 PM
Yup. Printers have similar distinctive patterns, is my understanding.

nightmarepatrol
2011-Jan-15, 07:18 PM
Yes they do, if memory serves me correct it was done at he urging of the US government to help prevent passport fraud. Anyhow for more information this (http://www.eff.org/issues/printers) would be a good place to start reading.

Strange
2011-Jan-15, 11:22 PM
I have read that modern photocopiers also embed identifying information in copies, also as an anti-fraud measure.

Middenrat
2011-Jan-16, 04:57 AM
At least up until a few years ago - my latest recollection - a near-invisible trace of dots was printed at the end of every task which encoded the printer's identity, similar to the encoding of Postcodes on envelopes in automated mailsorting machines.

Nowhere Man
2011-Jan-16, 01:57 PM
This is probably what you're looking for. Printer steganography. (http://en.wikipedia.org/wiki/Printer_steganography)

Fred

JustAFriend
2011-Jan-16, 11:06 PM
Yup, for a long time.

15 years ago I worked for a company helping to run the graphics dept and we installed a high-end color copier/printer to proof pages.
They explained to us in training that every sheet had ID codes embedded for anti-counterfeiting and other security measures to keep you from copying currency (so many violations and they were required to call the Treasury Dept.)

It stopped on us several times with the violation code and we figured out that it was keying on light reflection shapes in the eyeballs as we were trying to print out some employee photos that matched the same shapes on scanned currency!

But yeah they can trace nearly anything back to the printer that created it.

tashirosgt
2011-Jan-17, 02:13 AM
The self-identification features of modern machines is interesting. There could be some interesting plot twists where someone counterfeits them. Perhaps they could print a document and tape over the main text to get the "signature" of a printer. Then they could print something else on the page using a different printer.

I suppose a person who knew how to hack into the processor of a printer could make it print a fake signature.

If we have some text is cut out of a printed document and not the whole document, is the way that characters are formed unique enough to trace the text to a particular machine? I'd think that things like the drums on laser printers could have small imperfections that would show up in their printing.

jamesabrown
2011-Jan-18, 03:38 PM
Don't digital photos embed the serial number etc. of the camera used to make them?

HenrikOlsen
2011-Jan-18, 09:01 PM
Up until you used a program which doesn't keep that information to modify the image.
I'm actually slightly irritated with GIMP for keeping such information as focal length even after I scaled and cropped the image, operations which invalidates that information.

Ara Pacis
2011-Jan-19, 07:55 AM
If we have some text is cut out of a printed document and not the whole document, is the way that characters are formed unique enough to trace the text to a particular machine? I'd think that things like the drums on laser printers could have small imperfections that would show up in their printing.

Even if they do, you're not printing from the entire surface unless you print a large block of 100% solid color/black. The chance that particular imperfection will line up on a similar glyph is probably unlikely, unless you try multiple pages filled with the same character at the same column location.

Of course, even if there is identifying information on the printer, "they" have to be able to trace the printer to a specific person. So, go to the nearest large city and pay cash and don't give any identifying information, avoid security cameras and wear a disquise and wear gloves. Come to think of it, I think I've had customers like that before... I wonder what they did with it.

jokergirl
2011-Jan-24, 10:16 AM
I have yet to see a CSI show that uses the EXIF info for picking out the camera model and pinpointing the suspect with the expensive DSLR.
(and anyway, it can be faked - not sure the clue would hold up in court)

;)

HenrikOlsen
2011-Feb-01, 07:41 AM
Some DSLR's (I know it's available for my Canon 1000D) have an optional module which allows images to be cryptographically signed as they are taken, I expect exactly for such reasons as making them admissible as evidence in court and/or to prove copyright.

Admittedly, that's the opposite problem, namely proving it's your unmodified picture when you want to prove it is, as opposed to your suggestion of proving that it's your picture if you don't want it to be.