DIGITAL WATERMARKING Ngô Huy Phúc50701831 Trần Kim Lân50701259 Phạm Quốc Hiệp50700812.
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STEGANOGRAPHY
• Steganography (art of hidden writing)
– The art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message.
– The existence of information is secret.
• Histaeus used his slaves (information tattooed on a slave’s shaved head)
Initial Applications of information hiding
Passing Secret messages
STEGANOGRAPHY
DEFINITION
• The process of embedding information into a digital signal in a way that is difficult to remove.
• The signal may be text, images, audio, video.
• The information is also carried in the copy if the signal is copied.
LIFE-CYCLE PHASES
Attemp to extract
watermark from signal
Attemp to extract
watermark from signal
The marked signal is
modified
The marked signal is
modified
Produce watermarke
d signal
Produce watermarke
d signal
CLASSIFICATION
Digital watermarking techniques can be classified in many ways :
•Visibility•Robustness•Perceptibility•Capacity•Embedding method
VISIBILITY
• Visible– Text or a logo which identifies the owner of the
media.
• Invisible– Information is added as digital data to audio,
picture or video, but it cannot be perceived.– May be a form of Steganography.
ROBUSTNESS
• Robust – Resisted a designated a class of transformations.– Against adversary based attack.
(e.g. noise addition to images)– Used in copy protection application.
Example: Robust Private Spatial Watermarks
ROBUSTNESS
• Fragile– Fail to be detected after the slightest
modification.– Used for tamper detection.
Example: Blind Fragile DCT based Watermarks
ROBUSTNESS
• Semi-fragile– Resist benign tramsformations but fails detection
after malignant transformations.– Robust against user-level operation.
(e.g. image compression)– Used for detect malignant transformation.
Example: Blind Semi-fragile Spatial Watermarks
PERCEPTIBILITY
• Perceptible– Its presence in the marked signal is noticable, but
non-intrusive.
• Imperceptible– Original cover signal and the marked signal are
close to perceptually indistinguishable.
PERCEPTIBILITY
Stanford Bunny 3D Model Visible Watermarks in Bunny Model Distortion
Watermarking
Stanford Bunny 3D Model
Watermarking
Invisible Watermarks in Bunny Model Minimal Distortion
CAPACITY
• Depend on the length of the embedded message.
• Zero-bit long– Detect the presence or absence of the watermark.– A 1 denotes the presence. 0 denotes the absence.
• N-bit long– Modulated in the watermark.– Support multiple watermarks.
EMBEDDING METHOD
• Spread-spectrum– The marked signal is ontained by an additive
modification.– Modestly robust.– Have a low information capacity.
EMBEDDING METHOD
• Quantization type– The marked signal is ontained by quantization– Low robustness.– Have a high infoirmation capacity.
• Amplitude modulation– The marked signal is ontained by additive
modification similar to spread spectrum method.– Embedded in the spatial domain.
• As much information (watermarks) as possible.
Capacity• Only be accessible by authorized parties.
Security• Resistance against hostile/user dependent
changes Robustness• Invisibility Imperceptibility
DESIGN REQUIREMENTS
• A very simple yet widely used technique for watermarking images is to add a pattern on top of an existing image.
• Usually this pattern is an image itself - a logo or something similar.
SIMPLE WATERMARKING
The LSB technique is the simplest technique of watermark insertion.
• Consider a still image : each pixel of the color image has three components — red, green and blue.
• Allocate 3 bytes for each pixel. Then, each colour has 1 byte, or 8 bits.
LSB : LEAST SIGNIFICANT BIT
A pixel that is bright purple in colour can be showN as X0 = {R=255, G=0, B=255}
• Look at another pixel: X1 = {R=255, G=0, B=254}• Detecting a difference of 1 on a color scale of 256
is almost impossible for human eye.
Replace the color intensity information in the LSB with watermarking information, the image will still look the same to the naked eye.
LSB : LEAST SIGNIFICANT BIT
• Use a secret key to choose a random set of bits.• The more bits used in the host image, the more it
deteriorates.• Increasing the number of bits used though
obviously has a beneficial reaction on the secret image increasing its clarity.
LSB : LEAST SIGNIFICANT BIT
• Watermarking in the frequency domain involves selecting the pixels to be modified based on the frequency of occurrence of that particular pixel.
• Transform an image into the frequency domain. • A block-based DCT watermarking approach is
implemented. • An image is first divided into blocks and DCT is
performed on each block. The watermark is then embedded by selectively modifying the middle-frequency DCT coefficients.
FREQUENCY-BASED TECHNIQUES
What is DCT ?• Formally, the discrete cosine transform (DCT)
is a linear, invertible function F : RN -> RN (where R denotes the set of real numbers), or equivalently an invertible N × N square matrix
FREQUENCY-BASED TECHNIQUES
Discrete wavelet transform (DWT)• The image is separated into different resolution• The original image is high-pass filtered, yielding
the three large images, each describing local changes details in the original image
• It is then low-pass filtered and downscaled, yielding an approximation image.
• This image is high-pass filtered to produce the three smaller detail images.
• And low-pass filtered to produce the final approximation image in the upper-left.
WAVELET WATERMARKING TECHNIQUES
Embedding the watermark• The host image and watermark are transformed into
wavelet domain.• The transformed watermark coefficients were
embedded into those of host image at each resolution level with a secret key.
WAVELET WATERMARKING TECHNIQUES
• A Narrow-band signal is transmitted over a much larger bandwidth such that the signal energy presented in any signal frequency is undetectable
• A watermark is spread over many frequency bins so that the energy in one bin is very small and certainly undetectable.
SPREAD-SPECTRUM TECHNIQUES
• Because the watermark verification process knows the location and content of the watermark, it is possible to concentrate these weak signals into a single output with high SNR (Signal-to-noise ratio).
• Remark– To destroy such a watermark would require noise of
high amplitude to be added to all frequency bins.– The location of the watermark is not obvious.– Frequency regions should be selected that ensures
degradation of the original datafollowing any attack on the watermark.
SPREAD-SPECTRUM TECHNIQUES
References• Techniques and Applications of Digital
Watermarking and Content Protection Michael Arnold, Martin Schmucker, Stephen D. Wolthusen
• Steganography And Digital WatermarkingJonathan Cummins, Patrick Diskin, Samuel Lau and Robert Parlett, School of Computer Science, The University of Birmingham.
• Real-Time Digital Image WatermarkingSubramaniam Ganesan, Professor of Oakland University, Michigan
Foundations of Attacking
• 3 effects make detection of watermarking useless:
– Watermark cannot be detected.– False watermarks are detected.– Unauthorized detection of watermark.
Classification of Attacking
• Removal attacks• Geometrical attacks• Cryptographic attacks• Protocol attacks
Removal Attacks
• Most obvious method• Aim for complete removal of watermarking• Extreme form of this type is restore the
original object• Can happen unintentionally due to operations
in some certain applications.
Geometrical Attacks
• Do not actually remove the embedded watermark
• Intend to distort the watermark detector synchronization with the embedded information
Cryptographic Attacks
• Aim at cracking the security methods in watermarking schemes
• Finding a way to remove the embedded watermark information
• Embed misleading watermarks• High computational complexity
Protocol Attacks
• Aim at attacking the entire concept of the watermarking application
• First proposed in framework of invertible watermark
• The attacker subtracts his own watermark from the watermarked data and claims to be the owner
• Another type is copy attack
Some Methods
• Collusion Attack– Estimate the watermark from different works with
same watermark– The attackers can obtain an approximation of the
watermark by averaging the watermarked works
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