money tracing

[Reply to: hahn@lds.loral.com]

Tyler Yip enquires about the magnetic properties of ink used in U.S.
currency.  I believe the ink can be magnetized and the bill passed over
a magnetic scanner that recognizes a magnetic signature.  U.S. Tres.
has machines that very quickly pick counterfeits out of a stack of
bills using this method.

Other things U.S. Tres. does (and you can do) to recognize counterfeits
are:  1) Put the bill under UV light.  Cheap paper tends to fluoresce.
The real thing won't.  2) Look at the treasury seal (the only part of
the bill that is multi-colored).  Make sure that the denomination
printed over the seal is all black and all there.  3) Rub any of the
printing against a piece of typing paper hard enough so that the ink
from the bill stains the paper.  Now look at the bill where you rubbed
it.  Offset print jobs will smudge -- the real thing won't.

Europeans are now going a step further.  They are composing the
portrait out of concentric circles centered on one of the eyes.
If someone attempts to copy the bill using a digital scanner,
the resulting aliasing of the circles in the portrait will be
very noticeable to even a casual observer.  The are also using
colors chosen especially to foil color copiers.

|         (V)              |  "Tiger gotta hunt.  Bird gotta fly.
|   (^    (`>              |   Man gotta sit and wonder why, why, why.
|  ((\\__/ )               |   Tiger gotta sleep.  Bird gotta land.
|  (\\<   )   der Nethahn  |   Man gotta tell himself he understand."
|    \<  )                 |  
|     ( /                  |                Kurt Vonnegut Jr.
|      |                   |  
|      ^                   |