INDIAN INSTITUTE OF TECHNOLOGY, KHARAGPUR

OPTICAL WATERMARKING

for Printed document authentication

Under the guidance of

Prof.S.Mukhopadhay,

Prof. P.K.Biswas

By

A.Raghu Kiran,

Roll.no-10EC65R01

Need of printed document

authentication:

To fight counterfeiting and forgery

To distinguish original documents or product packages

by authorized parties from those which are produced

by expert forgers

Characteristics of Printed document

authentication techniques:

Must be robust against reverse engineering or cracking

techniques

Must be robust against duplicating the documents or packages

without noticeable distortion

Various information hiding techniques :

METHOD 1:

Modifying the position and shape of dots present in the dot

array of carrier image

METHOD 2:

Anti-photo copying by using Tri-branched and Divided lines

Limitations of information hiding

techniques:

Limited number of different decoders due to simple dot

matrix structure of carrier image

Encoding methods can be easily discovered by using a

microscope to view and analyze the dot or line patterns

OPTICAL WATERMARK:

It is a two-dimensional binary image

Constructed by the superposition of multiple two-

dimensional binary images(referred to as layers), each

with different carrier structural patterns embedding

various hidden information.

The hidden information is embedded into each layer

using phase modulation.

FEATURES OF OPTICAL WATERMARK:

Generalization of carrier structure from simple dot pattern to

curves and further to generic random dot patterns, so as to

increase the complexity and increase the number of different

decoders

Superposition of multiple logical carrier images, each encoded

with their own hiding information, thus giving extreme

difficulty in reproducing the same document

Multiple layer structure of

optimal watermark

Basis of Optical Watermark

Different types of optical

watermark layers:

Classified based on information carrier structure used

Basic watermark layer

Co-ordinate mapping of basic watermark layer

Secret sharing watermark layer

Basic watermark layer:

Information carrier structure is simple dot array

Dot array can be represented by a reflectance function

Tx, Ty represent period of dot array in X and Y directions

Dx, Dy are widths of dot in two directions

Illustration of dot array

parameters:

Phase modulation to embed latent

images into information structure:

Modulation is done by shifting the latent image with a

half period of dot matrix in either X-direction or Y-

direction

The phase modulated structure w(x,y) can be written as

Modulation of T in X- axis

Demodulation can be done by using a set of reference line

grating with same frequency, superposed at a right angle

Reference line grating can be given as

Tr,Dr are period of line grating and width of line

Demodulated function is

d(x,y) = fr(x,y).w(x,y)

Demodulation:

DEMODULATION RESULT:

Dark character “T” with white background after de-modulation

Reference line grating for

demodulation (here angle ᶱ~0o

L1, L2 and L3 are watermark layerswith the same frequency but differentorientations.W is the superposition of L1, L2 andL3

Illustration of superposition of multiple watermark layers

Co-ordinate mapping of basic

watermark layer:

By applying co-ordinate mapping to the information

carrier structure, dimensionality of carrier structure is

increased

With different co-ordinate mapping functions, the

mapped watermark layer will have different complexity

Non-linear mapping significantly increases the

complexity of the watermark layer

A -> the original watermark layer

B the mapped watermark layer

C is the mapped decoder corresponding to the mapped

watermark layer in B

The decoded result by superposition of decoder in C on top

of the mapped watermark layer in B is shown in D

Secret sharing watermark layer:

By using random dot matrix as information carrier structure, the complexity of decoding keys is increased also security level is improved.

Information of latent image is randomly distributed to two parts.

Watermark layer is generated based on one part and decoder of this watermark layer is generated based on the other part.

Latent image is recoverable only when both watermark layer and decoder are present, thus security level is much improved.

Robustness of optical watermarking:

Multiple layer structure of optical watermark makes it extremely robust against reverse engineering attacks

Robustness increases with increase in complexity of information carrier structure

The order of robustness will be

Secret sharing watermark layer

Co-ordinate mapping watermark layer

Basic multiple watermark layer > >

Lower-right portionof a bill of lading, remotely printed by a supplier in their own office, with theseal and signature by the carrier (shipping company).

Applying one decodekey on the watermark in the seal reveals the bill of lading number, embeddedbeneath the signature.

Application example of online bill of lading

Application areas of optical

watermarking:

• On-line ticketing

• Certificates, identification documents

• Brand protection labels

• High value tickets

CONCLUSIONS:

An optical watermark for printed document authentication is presented

The watermark has a layered structure, consisting of multiple watermark layers, superposed on each other

The superposition of multiple layers effectively protects the optical watermark from reverse engineering individual watermark layers, and significantly enhances the security of the watermark

Three types of watermark layers are presented. They share the same information embedding method—phase modulation, while deferring by the information carrier structure

With a very high security optical watermark, based on digital printing, it is a new-generation anti-counterfeiting technology for both physical documents and online document processing and authentications

References:

Sheng Huang, Jian Kang Wu- ―Optical Watermarking for Printed

Document Authentication”, IEEE transactions on Information

Forensics and security, Vol:2,Issue:2, p.164-173, 2007.

S. Huang, ―Optical watermark,‖ Dept. Comput. Sci., National

Univ. of Singapore, Singapore, 2003.

F. A. P. Petitcolas, R. J. Anderson, and M. G. Kuhn, ―Information

hiding, a survey,‖ Proc. IEEE, Special Issue on Protection of

Multimedia Content, vol. 87, no. 7, pp. 1062–1078, Jul. 1999.

THANK YOU