digital watermark

2003. május 6.2003. május 6. Digital watermarkDigital watermark 11

Digital watermarkDigital watermark

Alfréd Rényi Institute of MathematicsAlfréd Rényi Institute of Mathematics László Csirmaz László Csirmaz Gyula Katona Gyula Katona Dezső Miklós Dezső Miklós Tibor Nemetz Tibor Nemetz

HP (HP (CompaqCompaq)) László MarsovskyLászló Marsovsky Attila Haraszti Attila Haraszti

Drótposta Ltd.Drótposta Ltd.


The problemThe problem

CurrentCurrent method method ofof identify identifyinging legal or high value legal or high value documents:documents:

Producing complicated patterns via printing technology (e.g. Producing complicated patterns via printing technology (e.g. banknotesbanknotes))

Applying holographic markers (e.g. tax stamps)Applying holographic markers (e.g. tax stamps) Specially prepared medium (e.g. embedding metal strips into Specially prepared medium (e.g. embedding metal strips into

paper)paper) At the present time, the most common technique of At the present time, the most common technique of

authentication uses serial numbers or in general authentication uses serial numbers or in general alphanumerical strings, rarely combined with pictograms. alphanumerical strings, rarely combined with pictograms. These can be copied or falsely created.These can be copied or falsely created.

We need a cheap automated solution!


The promiseThe promise

Finding a Finding a cheap solution (mark) ofcheap solution (mark) of identifyingidentifying leg legalal documents documents (bank cards, banknotes, stock certificates), (bank cards, banknotes, stock certificates), which is:which is:

UniqueUnique Very difficult or expensive to copy or duplicate Very difficult or expensive to copy or duplicate Can be measured Can be measured and processed and processed quicklyquickly A cA couple of hundred bits ouple of hundred bits can be generated can be generated as a check codeas a check code

Goal:Goal: An unforgeable, unique physical identifying markAn unforgeable, unique physical identifying mark A cheap device for reading the markA cheap device for reading the mark An algorithm making a unique and short (200-500 bits long) An algorithm making a unique and short (200-500 bits long)

extract from the pictureextract from the picture


Previous achievementsPrevious achievements

Different surfaces – that are actually difficult Different surfaces – that are actually difficult to copy, but often expensive – are to copy, but often expensive – are measured, and the results are stored in a measured, and the results are stored in a central database. The results of the control central database. The results of the control measurement are compared to the stored measurement are compared to the stored data.data.


NoveltiesNovelties

We do not store resultsWe do not store results The mark is cheap, but difficult to copyThe mark is cheap, but difficult to copy IT WORKSIT WORKS


The markThe mark


The reading deviceThe reading device


The methodThe method A three-dimensional thin layerA three-dimensional thin layer, a, a small mark small mark – –

which is very difficult or expensive to copy or which is very difficult or expensive to copy or duplicateduplicate – – is inseparably attached to the object. is inseparably attached to the object. This small mark will contain randomly positioned This small mark will contain randomly positioned small small objectsobjects..

Using digital imaging technology we test a Using digital imaging technology we test a photograph of the object, to see that the mark is photograph of the object, to see that the mark is 3 dimensional3 dimensional,, and not just a 2 dimensional copy and not just a 2 dimensional copy of a 3 dimensional object.of a 3 dimensional object.

Using different mathematical algorithmUsing different mathematical algorithmss wewe generate a unique number (check-code), generate a unique number (check-code), whichwhich can can clearlyclearly identify the object. identify the object.


The materialThe material

Into a tInto a thin (typically 0.3-1 mm thick)hin (typically 0.3-1 mm thick),, translucent translucent layer without a light reflecting coating small layer without a light reflecting coating small objectsobjects (e.g. glass beads)(e.g. glass beads) are are embeddedembedded..

Thin film

0.3-1 mm

Small (5-20 micrometer) glass beads (balls) coated or not


UnforgeableUnforgeable

Photos taken in diffuse and direct light


ResultsResults

The mark is very cheap, The mark is very cheap, asas we us we usee a material available a material available anywhere, anywhere, the price the price could be could be around 2-3 centsaround 2-3 cents..

The measuring The measuring device device is a WEB cam wis a WEB cam wiitthh speci specialal optic optics,s, which costswhich costs 200$-300$ 200$-300$

The stability of the ”code” is The stability of the ”code” is excellentexcellent. All measurement . All measurement was in a tolerance was in a tolerance ofof one digit one digit.. (plus, minus one pixel!) (plus, minus one pixel!)

The measurement time wThe measurement time wiitthh no non-n-optimized code is optimized code is around 10 seconds.around 10 seconds.

We have developed a method, which does not require We have developed a method, which does not require storing the code and checking the Hamming distance, storing the code and checking the Hamming distance, but regenerates the code every time on line, using a but regenerates the code every time on line, using a small piece of redundant information, like a PIN code.small piece of redundant information, like a PIN code.

digital watermark

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