To help ATMs - protection technology banknotes hidden water marks
In mid-October 2013 in Moscow, many users are faced with the refusal of ATMs of several major banks
take five thousandth bills through its ATMs. A little later, it turned out that this was due to the activities in Moscow
a gang of counterfeiters, who without hesitation, printed on a black and white copier 5-thousandths bills and pasted
over the makeshift security features.
Why ATMs have taken the black and white fake bills for real? It's very simple - they were
pasted elements of protection and automatic analyzers ATMs perceived these papers as authentic!
This is a good example of the lack conditional dependence
between the object and the means of protection.
This shortcoming affects many ways to protect your documents. Such as protection in the form of hologram stickers, embossed,
vpressovyvaniya metal wire and others. Substitution of object identification, while maintaining the "surface " of the security element,
does not lead to a conclusion about a fake document.
However, the production of banknotes used a sophisticated way to protect both the "shift effect" that provides surveillance
letters "PP" or apply hidden
Moire patterns that occur when you lean cuts.
The above methods are characterized as effective hidden
means of defense, but unsuitable for implementation in automatic detectors
the authenticity of banknotes. The most important device ATMs operating in the receive mode of cash, are automatic detectors, which are supplied
the optical sensors for monitoring card watermarking optically banknotes absorbance of banknotes,
programmable analyzers pattern and spatial spectrum (Fourier
) Image bills, etc. It is known that, even banknote counters "Speed" table
16 have levels of sensitivity in detecting mode, the optical density of banknotes. Examples of histogram quantization levels (digital representation of the optical density) photos banknote is shown below:
Arsenal above methods of protection is quite impressive and is quite suitable for the implementation of technology hide
in the " body" of images of banknotes. Paper bills, while must have sufficient optical density range
( quantization levels ). Hidden protective elements may be regulated list of visual data:
serial number of the banknote denomination notes, the date of manufacture of the banknote, a facsimile of the responsible person,
Repeat pattern or watermark banknote. One such technology allows to embed in the image on paper or plastic carriers
watermarks ( HWM ) as an analogue holograms.
In accordance with this technology (Embedding HWM: holographic approach
), the container ( "body" ) banknote image is being implemented hologram hidden
of the security element. Visually, a sufficient increase
Image container, it is possible to observe an interference pattern similar in appearance to the moire stripes.
An example of such a pattern is shown in an enlarged fragment images deposited on a plastic carrier
The following figure shows a photograph of a fragment banknote with built hidden
data in facsimile:
At the stage of the bill validator to recover hidden data necessary to make a two-dimensional transformation
hologram and performing a spatial sampling.
In real time, this procedure is implemented using digital signal processors (DSPs) for the fraction of a second.
The recovery process hidden
data can be observed as the restored object and its holographic
Image. The figure below shows the result of a reconstruction of the hologram facsimile:
The technology brings together the identity of the object (the image on the banknotes)
and Remedies (HWM) in a single unit. Event object substitution
fake identification becomes conditionally dependent
regarding protection - HWM.
Thus, in response to the lack of HWM is the conclusion of a fake script. If you add cryptographic security HWM,
it will attempt to break useless
on a practical level.
What remains to be seen about the HWM: