A digital watermark is a kind of marker covertly embedded in a noise-tolerant
signal
In signal processing, a signal is a function that conveys information about a phenomenon. Any quantity that can vary over space or time can be used as a signal to share messages between observers. The '' IEEE Transactions on Signal Processing' ...
such as audio, video or image data. It is typically used to identify ownership of the copyright of such signal. "Watermarking" is the process of hiding digital information in a
carrier signal
In telecommunications, a carrier wave, carrier signal, or just carrier, is a waveform (usually sinusoidal) that is modulated (modified) with an information-bearing signal for the purpose of conveying information. This carrier wave usually has ...
; the hidden information should,
[Ingemar J. Cox: ''Digital watermarking and steganography''. Morgan Kaufmann, Burlington, MA, USA, 2008] but does not need to, contain a relation to the carrier signal. Digital watermarks may be used to verify the authenticity or integrity of the carrier signal or to show the identity of its owners. It is prominently used for tracing
copyright infringement
Copyright infringement (at times referred to as piracy) is the use of works protected by copyright without permission for a usage where such permission is required, thereby infringing certain exclusive rights granted to the copyright holder, ...
s and for
banknote
A banknote—also called a bill (North American English), paper money, or simply a note—is a type of negotiable instrument, negotiable promissory note, made by a bank or other licensed authority, payable to the bearer on demand.
Banknotes w ...
authentication.
Like traditional
physical watermarks, digital watermarks are often only perceptible under certain conditions, e.g. after using some algorithm.
[Frank Y. Shih: ''Digital watermarking and steganography: fundamentals and techniques''. Taylor & Francis, Boca Raton, FL, USA, 2008] If a digital watermark distorts the carrier signal in a way that it becomes easily perceivable, it may be considered less effective depending on its purpose.
Traditional watermarks may be applied to visible media (like images or video), whereas in digital watermarking, the signal may be audio, pictures, video, texts or 3D models. A signal may carry several different watermarks at the same time. Unlike
metadata that is added to the carrier signal, a digital watermark does not change the size of the carrier signal.
The needed properties of a digital watermark depend on the
use case
In software and systems engineering, the phrase use case is a polyseme with two senses:
# A usage scenario for a piece of software; often used in the plural to suggest situations where a piece of software may be useful.
# A potential scenari ...
in which it is applied. For marking media files with copyright information, a digital watermark has to be rather robust against modifications that can be applied to the carrier signal. Instead, if integrity has to be ensured, a fragile watermark would be applied.
Both
steganography
Steganography ( ) is the practice of representing information within another message or physical object, in such a manner that the presence of the information is not evident to human inspection. In computing/electronic contexts, a computer file, ...
and digital watermarking employ steganographic techniques to embed data covertly in noisy signals. While steganography aims for imperceptibility to human senses, digital watermarking tries to control the robustness as top priority.
Since a digital copy of data is the same as the original, digital watermarking is a passive protection tool. It just marks data, but does not degrade it or control access to the data.
One application of digital watermarking is ''source tracking''. A watermark is embedded into a digital signal at each point of distribution. If a copy of the work is found later, then the watermark may be retrieved from the copy and the source of the distribution is known. This technique reportedly has been used to detect the source of illegally copied movies.
History
The term "Digital Watermark" was coined by Andrew Tirkel and Charles Osborne in December 1992. The first successful embedding and extraction of a
steganographic spread spectrum watermark was demonstrated in 1993 by Andrew Tirkel, Charles Osborne and Gerard Rankin.
Watermarks are identification marks produced during the paper making process. The first watermarks appeared in Italy during the 13th century, but their use rapidly spread across Europe. They were used as a means to identify the paper maker or the trade guild that manufactured the paper. The marks often were created by a wire sewn onto the paper mold. Watermarks continue to be used today as manufacturer's marks and to prevent forgery.
Applications
Digital watermarking may be used for a wide range of applications, such as:
*
Copyright protection
* Source tracking (different recipients get differently watermarked content)
* Broadcast monitoring (television news often contains watermarked video from international agencies)
* Video authentication
*
Software crippling on
screencasting and
video editing software
Video editing software, or a video editor is software used performing the post-production video editing of digital video sequences on a non-linear editing system. It has replaced traditional flatbed celluloid film editing tools and analog video t ...
programs, to encourage users to purchase the full version to remove it.
*ID card security
*Fraud and Tamper detection.
* Content management on
social network
A social network is a social structure made up of a set of social actors (such as individuals or organizations), sets of dyadic ties, and other social interactions between actors. The social network perspective provides a set of methods for ...
s
Digital watermarking life-cycle phases
The information to be embedded in a signal is called a digital watermark, although in some contexts the phrase digital watermark means the difference between the watermarked signal and the cover signal. The signal where the watermark is to be embedded is called the ''host'' signal. A watermarking system is usually divided into three distinct steps, embedding, attack, and detection. In embedding, an algorithm accepts the host and the data to be embedded, and produces a watermarked signal.
Then the watermarked digital signal is transmitted or stored, usually transmitted to another person. If this person makes a modification, this is called an ''attack''. While the modification may not be malicious, the term attack arises from copyright protection application, where third parties may attempt to remove the digital watermark through modification. There are many possible modifications, for example, lossy compression of the data (in which resolution is diminished), cropping an image or video, or intentionally adding noise.
''Detection'' (often called extraction) is an algorithm which is applied to the attacked signal to attempt to extract the watermark from it. If the signal was unmodified during transmission, then the watermark still is present and it may be extracted. In ''robust'' digital watermarking applications, the extraction algorithm should be able to produce the watermark correctly, even if the modifications were strong. In ''fragile'' digital watermarking, the extraction algorithm should fail if any change is made to the signal.
Classification
A digital watermark is called ''robust'' with respect to transformations if the embedded information may be detected reliably from the marked signal, even if degraded by any number of transformations. Typical image degradations are JPEG compression, rotation, cropping, additive noise, and
quantization. For video content, temporal modifications and MPEG compression often are added to this list. A digital watermark is called ''imperceptible'' if the watermarked content is perceptually equivalent to the original, unwatermarked content.
In general, it is easy to create either robust watermarks—or—imperceptible watermarks, but the creation of both robust—and—imperceptible watermarks has proven to be quite challenging.
Robust imperceptible watermarks have been proposed as a tool for the protection of digital content, for example as an embedded ''no-copy-allowed'' flag in professional video content.
Digital watermarking techniques may be classified in several ways.
Robustness
A digital watermark is called "fragile" if it fails to be detectable after the slightest modification. Fragile watermarks are commonly used for tamper detection (integrity proof). Modifications to an original work that clearly are noticeable, commonly are not referred to as watermarks, but as generalized
barcode
A barcode or bar code is a method of representing data in a visual, Machine-readable data, machine-readable form. Initially, barcodes represented data by varying the widths, spacings and sizes of parallel lines. These barcodes, now commonly refe ...
s.
A digital watermark is called ''semi-fragile'' if it resists benign transformations, but fails detection after malignant transformations. Semi-fragile watermarks commonly are used to detect malignant transformations.
A digital watermark is called ''robust'' if it resists a designated class of transformations. Robust watermarks may be used in copy protection applications to carry copy and no access control information.
Perceptibility
A digital watermark is called ''imperceptible'' if the original cover signal and the marked signal are perceptually indistinguishable.
A digital watermark is called ''perceptible'' if its presence in the marked signal is noticeable (e.g. digital on-screen graphics like a network logo, content bug, codes, opaque images). On videos and images, some are made transparent/translucent for convenience for consumers due to the fact that they block portion of the view; therefore degrading it.
This should not be confused with ''perceptual'', that is, watermarking which uses the limitations of human perception to be imperceptible.
Capacity
The length of the embedded message determines two different main classes of digital watermarking schemes:
* The message is conceptually zero-bit long and the system is designed in order to detect the presence or the absence of the watermark in the marked object. This kind of watermarking scheme is usually referred to as ''zero-bit'' or ''presence watermarking schemes''.
* The message is an n-bit-long stream
, with
or
and is modulated in the watermark. These kinds of schemes usually are referred to as multiple-bit watermarking or non-zero-bit watermarking schemes.
Embedding method
A digital watermarking method is referred to as ''
spread-spectrum'' if the marked signal is obtained by an additive modification. Spread-spectrum watermarks are known to be modestly robust, but also to have a low information capacity due to host
interference.
A digital watermarking method is said to be of ''quantization type'' if the marked signal is obtained by quantization. Quantization watermarks suffer from low robustness, but have a high information capacity due to rejection of host interference.
A digital watermarking method is referred to as ''
amplitude modulation'' if the marked signal is embedded by additive modification which is similar to spread spectrum method, but is particularly embedded in the spatial domain.
Evaluation and benchmarking
The evaluation of digital watermarking schemes may provide detailed information for a watermark designer or for end-users, therefore, different evaluation strategies exist. Often used by a watermark designer is the evaluation of single properties to show, for example, an improvement. Mostly, end-users are not interested in detailed information. They want to know if a given digital watermarking algorithm may be used for their application scenario, and if so, which parameter sets seems to be the best.
Cameras
Epson
Seiko Epson Corporation, or simply known as Epson, is a Japanese multinational electronics company and one of the world's largest manufacturers of computer printers and information- and imaging-related equipment. Headquartered in Suwa, Nagano ...
and
Kodak
The Eastman Kodak Company (referred to simply as Kodak ) is an American public company that produces various products related to its historic basis in analogue photography. The company is headquartered in Rochester, New York, and is incorpor ...
have produced cameras with security features such as the Epson PhotoPC 3000Z and the Kodak DC-290. Both cameras added irremovable features to the pictures which distorted the original image, making them unacceptable for some applications such as
forensic evidence in court. According to Blythe and Fridrich, "
ither camera can provide an undisputable proof of the image origin or its author".
A secure digital camera (SDC) was proposed by Saraju Mohanty, et al. in 2003 and published in January 2004. This was not the first time this was proposed.
Blythe and Fridrich also have worked on SDC in 2004
for a
digital camera
A digital camera is a camera that captures photographs in digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film. Digital cameras are now widely incorporated into mobile devic ...
that would use lossless watermarking to embed a
biometric
Biometrics are body measurements and calculations related to human characteristics. Biometric authentication (or realistic authentication) is used in computer science as a form of identification and access control. It is also used to identify ...
identifier together with a
cryptographic hash.
Reversible data hiding
''Reversible data hiding'' is a technique which enables images to be authenticated and then restored to their original form by removing the digital watermark and replacing the image data that had been overwritten. This would make the images acceptable for legal purposes. The US Army also is interested in this technique for authentication of
reconnaissance
In military operations, reconnaissance or scouting is the exploration of an area by military forces to obtain information about enemy forces, terrain, and other activities.
Examples of reconnaissance include patrolling by troops ( skirmishe ...
images.
Watermarking for relational databases
Digital watermarking for
relational database
A relational database is a (most commonly digital) database based on the relational model of data, as proposed by E. F. Codd in 1970. A system used to maintain relational databases is a relational database management system (RDBMS). Many relatio ...
s has emerged as a candidate solution to provide copyright protection, tamper detection, traitor tracing, and maintaining integrity of relational data. Many watermarking techniques have been proposed in the literature to address these purposes. A survey of the current state-of-the-art and a classification of the different techniques according to their intent, the way they express the watermark, the cover type, granularity level, and verifiability was published in 2010 by Halder et al. in the
Journal of Universal Computer Science
The ''Journal of Universal Computer Science'' (''J.UCS'') is a monthly peer-reviewed open-access scientific journal covering all aspects of computer science.
History
The journal was established in 1994 and is published by the J.UCS Consortium ...
.
See also
*
Coded Anti-Piracy
*
Copy attack
*
EURion constellation
The EURion constellation (also known as Omron rings or doughnuts) is a pattern of symbols incorporated into a number of secure documents such as banknotes and ownership title certificates designs worldwide since about 1996. It is added to help ...
*
Pattern Recognition (novel)
*
Steganography
Steganography ( ) is the practice of representing information within another message or physical object, in such a manner that the presence of the information is not evident to human inspection. In computing/electronic contexts, a computer file, ...
*
Traitor tracing
*
Watermark (data file)
*
Audio watermark
*
Digital on-screen graphic
*
Automatic content recognition
Automatic content recognition (ACR) is a technology to identify content played on a media device or present within a media file. Devices implementing ACR can allow the device or the manufacturer to collect content consumption information automatic ...
References
Further reading
ECRYPT report: Audio Benchmarking Tools and SteganalysisECRYPT report: Watermarking Benchmarking* Jana Dittmann, David Megias, Andreas Lang, Jordi Herrera-Joancomarti; ''Theoretical framework for a practical evaluation and comparison of audio watermarking schemes in the triangle of robustness, transparency and capacity''; In: Transaction on Data Hiding and Multimedia Security I; Springer LNCS 4300; Editor Yun Q. Shi; pp. 1–40; ,200
PDF*
* Patrick Bas, Teddy Furon, François Cayre, Gwenaël Doërr, Benjamin Mathon, "Watermarking Security, Fundamentals, Secure Designs and Attacks", Springer Briefs in Electrical and Computer Engineering, 2016,
External links
{{DEFAULTSORT:Digital Watermarking
Authentication methods
Watermarking
Digital photography