robust undetectable interference watermarks
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Robust Undetectable Interference Watermarks. Ryszard Grz ąślewicz (WUT) Mirosław Kutyłowski (WUT) Jarosław Kutyłowski (HNI) Wojciech Pietkiewicz (WUT). Introduction. Motivation undetectable watermarks cannot be detected in an image - PowerPoint PPT PresentationTRANSCRIPT
Jaroslaw Kutylowski 1
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and Complexity
Robust Undetectable Interference Watermarks
Ryszard Grząślewicz (WUT)
Mirosław Kutyłowski (WUT)
Jarosław Kutyłowski (HNI)
Wojciech Pietkiewicz (WUT)
Jaroslaw Kutylowski 2
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityIntroduction
Motivation• undetectable watermarks cannot be detected in an image• only the owner can prove his rights to an image using
a secret private key• not suited for web crawlers
Key features of our scheme• watermarks encoded in spatial domain• resistant against attack preserving distance between points
(filtering, rotation, JPEG compression)• resistance against some attacks changing distance between points• watermark can be reconstructed from a small part of image• original image not needed for reconstruction• large computational effort for reconstruction needed
Jaroslaw Kutylowski 3
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityPhysical motivation
Interference – Young‘s experiment
Jaroslaw Kutylowski 4
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityScheme overview
Watermark image
Interference image
Watermarked image
Reconstructed watermark image
Cover image
Jaroslaw Kutylowski 5
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityConstruction of simple interference image
Watermark image• all black with some white points• white points are light source• set of white points
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Jaroslaw Kutylowski 6
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityConstruction of simple interference image
Interference image• interference image is placed at distance
on top of watermark image• each “light source” from influences
each point of interference image • distance and determine strength
of influence
• this is approximation of real physicalinterference image
• drawback: visible pattern
Jaroslaw Kutylowski 7
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityConstruction of encrypted interference image
Interference image• consider the influence of one point from• previously it influenced a point at distance with
• a ring at distance consists of cells of size • intensity of each cell defined by value of hash function• the angle is taken modulo – repetition of the same sequence• key is needed for computation of values
• interference image does not containvisible patterns
Jaroslaw Kutylowski 8
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityScheme overview
Watermark image
Interference image
Watermarked image
Reconstructed watermark image
Cover image
Jaroslaw Kutylowski 9
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityReconstruction of watermark
General idea• determine the intensity of each point of the watermark image
– take the watermarked image (cover image + interference image)
– generate interference image for point
– compare them
– if there is strong “similarity” – assign a high value
watermarked image interference image for
Low similarity
small pixel value
High similarity
large pixel valueExample with simple interference
image not with encrypted – usually the encrypted would be used
Jaroslaw Kutylowski 10
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityReconstruction of watermark
Idea (continued)• look for the highest valued points• check whether these points form a valid watermark
– use equilateral triangles
– certain number of triangles of specific edge length must be found to form a watermark
Properties• for the points actually in
– there will be a large similarity between the watermarked image and the interference image
• there are points to check• for each point operations are needed to compare the images• key is needed for reconstruction
Jaroslaw Kutylowski 11
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityReconstruction of watermark
Additional operations• the reconstruction must be repeated for all rotations with degree
– this yields resistance against rotations of the image
• the scale factor of the image must be determined– take a small part of the image
– there should be at least one “white point” from in this part
– check different scale factors and perform reconstruction of this image part for it
– determine scale factor with largest peak value – this peak corresponds to a white point from the watermark
– perform full reconstruction with this scale factor
Jaroslaw Kutylowski 12
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityExperimental results
Evaluation against StirMark 3• 77 of 89 tests passed• Cropping – all passed• Removing rows/columns – only lighter one passed• Flip – all passed• Scaling – all passed• Change aspect ratio – all passed• Rotation with cropping – for rotation smaller than 30% passed• Rotation with cropping and scalling – for rotation smaller than 30% passed• Shearing – only simple ones passed• Linear transformations – not passed• StirMark – not passed• Gaussian filtering – all passed• Sharpening – all passed• Median filtering – all passed• LRAttack – all passed• JPEG compression – all passed
Jaroslaw Kutylowski 13
HEINZ NIXDORF INSTITUTEUniversity of Paderborn
Algorithms and ComplexityConclusions
Results• robustness against attacks basing on filtering and local editions
of image shown• robustness against some linear transformations (rotating, scaling)
shown
Further work• methods for detection of general linear transformations needed• methods for detection of nonlinear transformations needed