Watermarking and Steganography

Watermarking and Steganography

• Watermarking is the practice of hiding a message about an image, audio clip, video clip, or other work of media within that work itself.

• Steganography is the art of writing in cipher, or in character, which are not intelligible except to persons who have the key. In computer terms, steganography has evolved into the practice of hiding a message within a larger one in such a way that others cannot discern the presence or contents of the hidden message.

Examples of Watermarking and Steganography

Difference between Watermarking and Steganography

• Watermarking

Insert a logo, pattern, a

message, and etc. into

an image, audio, video

to claim the ownership.

• Steganography

Put a cover image,

audio, video, and etc.

on a secret message to

protect the secrecy

during the transmission.

Strategies of Watermarking (1/2)

• Cox et al. (1997)

A watermark may contain additional

information, including the identity of the

purchaser of a particular copy of the material.

In order to be effective, a watermark should

be:

unobtrusive, robust, universal, unambiguous

Criteria of WatermarkingUnobtrusive: The watermark should be perceptually invisible, or its presence should not interfere with the work being protected.

Robust: The watermark must be difficult (hopefully impossible) to remove. In particular, the watermark should be robust to

Common signal processing: enhancement, requantization, resampling,

recompression, dithering, and etc.

Common geometric distortions: rotation, scaling, translation, cropping.

Subterfuge Attacks: Collusion and Forgery The watermark should be robust to collusion by multiple individuals who each possesses a watermarked copy of the data.

Universal The same digital watermarking algorithm should apply to all three media under consideration: i.e., audio, image, video.

Unambiguous Retrieval of the watermark should unambiguously identity the owner.

Strategies of Watermarking (2/2)

Wolfgang, Podilchuk, and Delp (1999) Three principles that characterize perceptually based watermarks:

Transparency: the watermark is not visible in the image under typical viewing conditions.

Robustness to attacks: the watermark can still be detected after the

image has undergone linear or nonlinear operations such as those mentioned above.

Capacity: the watermarking technique must be of allowing multiple watermarks to be inserted in an image, with each watermark still being independently verifiable.

Criteria for Watermarking• For the ownership authentication and/or protection of intellectual property. E

xperiments of watermarking studies may include at least the following tasks:• a watermark definition (generative or acquired)

• watermark embedding or insertion scheme

• extraction, detection, and/or verification of a watermark

• Experiments for testing transparency (unobstrusion~flexibility)

• Experiments for testing robustness to image operations, such as compression

• Experiments for testing collusion or multiple colluders

• PSNR values between the original and watermarked imagesPSNR values between the original and attacked images

Major Tasks of Watermarking and Steganography

• Watermarking

Watermark generator

Embedder

Detector

• Steganography

• Selection of a cover image, video, audio

• Embedding• Extraction

3-Scale Wavelet Transforms

• Haar transform

• 5/3 wavelet transform

• Daubechies Four

• 9/7 wavelet transform

3-Scale Wavelet Transforms