An image with visible digital watermarking. The text "Brian Kell 2006" can be seen across the center of the image.

Digital watermarking is a technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. Such hidden message is a group of bits describing information pertaining to the signal or to the author of the signal (name, place, etc.). The technique takes its name from watermarking of paper or money as a security measure. Digital watermarking can be a form of steganography, in which data is hidden in the message without the end user's knowledge. Image File history File links Download high resolution version (1920x2560, 1216 KB) Summary An example of an image with visible digital watermarking, identifying the photographer of the image (me). ... Image File history File links Download high resolution version (1920x2560, 1216 KB) Summary An example of an image with visible digital watermarking, identifying the photographer of the image (me). ... Copyright symbol Copyright is a set of exclusive rights regulating the use of a particular expression of an idea or information. ... This Crown & CA (for Crown Agent) watermark was standard for postage stamps of the British colonies from the 1880s to the 1920s. ... Steganography is 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; this is in contrast to cryptography, where the existence of the message itself is not disguised, but the content is obscured. ...

While the addition of the hidden message to the signal does not restrict that signal's use, it provides a mechanism to track the signal to the original owner.

A watermark can be classified into two sub-types: visible and invisible. Visible watermarks change the signal altogether such that the watermarked signal is totally different from the actual signal, e.g., adding an image as a watermark to another image. Stock photography agencies often add a watermark in the shape of a copyright symbol ("©") to previews of their images, so that the previews do not substitute for high-quality copies of the product included with a license. Stock photography consists of existing photographs that can be licensed for specific uses. ...

Invisible watermarks do not change the signal to a perceptually great extent, i.e., there are only minor variations in the output signal. An example of an invisible watermark is when some bits are added to an image modifying only its least significant bits. Invisible watermarks that are unknown to the end user are steganographic. The binary representation of decimal 149, with the lsb highlighted. ... Steganography is 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; this is in contrast to cryptography, where the existence of the message itself is not disguised, but the content is obscured. ...

Another application is to protect digital media by fingerprinting each copy with the purchaser's information. If the purchaser makes illegitimate copies, these will contain his name. Fingerprints are an extension to watermarking principle and can be both visible and invisible.

There are various spatial and frequency domain techniques used for adding watermarks to and removing them from signals. Purely spatial techniques are not robust to some attacks to the signal like cropping and zooming, whereas most frequency domain techniques and mixed-domain techniques are quite robust to such attacks. Frequency domain is a term used to describe the analysis of mathematical functions with respect to frequency. ...

The communication of a digital watermark may be viewed as an exercise in digital communication. The message bits are encoded and embedded in a suitable carrier. The properties that are desired of the watermark, such as imperceptability, robustness to noise and to image editing such as cropping and rotation are the factors that drive the choice of carrier. In robust watermarks, it is the combination of low signal amplitude (because the watermark is invisible) and large bandwidth (because images are typically quite large), as well as the relatively short length of the message, that dictates the use of spread spectrum for encoding the message bits. Spread spectrum is a robust and secure form of communication. In image watermarking, the spread spectrum signal is typically placed in the frequency domain to produce a watermark that is immune to image processing. Digital communication, as opposed to analogue communication refers to all emerging communications and technologies via a digital platform usually combining text, graphics, sound, and video, utilising computer or mobile technology. ... Spread-spectrum telecommunications is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. ...

Image compression techniques, such as JPEG, inspired the use of the frequency domain for embedding imperceptible watermarks in images. The first frequency domain technique was devised by Scott Burgett, Eckhard Koch, and Jian Zhao, who utilized the Discrete Cosine Transform. This and other transforms, such as the Wavelet transform, were used by Joseph O Ruanaidh, who later developed rotation and translation invariant watermarks based on the Fourier transform. Ingemar Cox popularized the use of Spread spectrum techniques for robust watermarking. Geoff Rhoads, Chief Technical Officer and founder of Digimarc Corporation, developed the PictureMarc technology. Image compression is the application of data compression on digital images. ... In computing, JPEG (pronounced JAY-peg; IPA: ) is a commonly used standard method of compression for photographic images. ... 2-D DCT compared to the DFT The discrete cosine transform (DCT) is a Fourier-related transform similar to the discrete Fourier transform (DFT), but using only real numbers. ... The wavelet transform is a transformation to basis functions that are localized in scale and in time as well (where the Fourier transform is only localized in frequency, never giving any information about where in space or time the frequency happens). ... Dr. Joseph Ó Ruanaidh was born in London, England, in 1967, of Irish parents and was mainly raised in Ballyfermot, Dublin, Republic of Ireland. ... In mathematics, the Fourier transform is a certain linear operator that maps functions to other functions. ... Spread-spectrum telecommunications is a technique in which a signal is transmitted in a bandwidth considerably greater than the frequency content of the original information. ... Digimarc Corporation, commonly known as Digimarc, (NASDAQ: DMRC) is the leading provider in secure government issued credentials. ...

The BBC have recently started watermarking their Doctor Who images because individuals were selling prints of them on Ebay. For other uses, see BBC (disambiguation). ... The correct title of this article is . ...

History

The term "digital watermark" was first coined in 1992 by Andrew Tirkel and Charles Osborne, in their paper: A.Z.Tirkel, G.A. Rankin, R.M. Van Schyndel, W.J.Ho, N.R.A.Mee, C.F.Osborne. “Electronic Water Mark”. DICTA 93, Macquarie University. p.666-673.

Actually, the term used by Tirkel and Osborne was originally used in Japan-- from the Japanese-- "denshi sukashi" -- literally, an "electronic watermark".

Paul LevinsonFuture of the Information Revolution (1997), where he called for the use "smart patent numbers" (p. 202), or the embedding of electronic chips in every piece of technology, which would give an updated listing of all of its inventors. Paul Levinson, 2002 Paul Levinson (b. ...

Whereas a digital watermark can be a form of steganography, e.g., the digital watermark is hidden in plain view. Functionally, the term "digital watermark" is used to describe that which enables differentiation between copies of the "same" content in an imperceptible manner. Many watermarking systems take this a step further, hiding the data so that attempts at erasure results in degradation of the quality of the content.

See also

• ImageMagick (for adding visible watermarks)
• Copy attack
• Watermark (data file)

ImageMagick is a free software suite for the creation, modification and display of bitmap images. ... Copy Attack The copy attack is an attack on certain digital watermarking systems proposed by M. Kutter, S. Voloshynovskiy, and A. Herrige in a paper presented in January, 2000 at the Photonics West SPIE convention . In some scenarios, a digital watermark is added to a piece of media such as... This article needs to be cleaned up to conform to a higher standard of quality. ...

Software for adding visible watermarks

• Visual Watermark - Easy-to-use batch photo watermarking software.
• Picture Shark - Free alternative to Visual Watermark.
• uMark - Batch image watermarking software for windows from India.
• Photo Watermark Professional - Supports a combination of batch watermarking, cropping, converting, resizing, renaming, enhancing, framing and printing.
• AiS Watermark Pictures Protector - ActiveX component for visible watermarking.

External links

• Watermarking World - Premier site servicing the scientific Digital Watermarking community by Dr. Martin Kutter
• Watermarking Search Engine - search engine customized for best search in digital watermarking
• Digital Watermarking Alliance - Furthering the Adoption of Digital Watermarking
• Digital Watermarking & Data Hiding research papers at Forensics.nl
• Stirmark Watermarking robustness test developed by Fabien Petitcolas, Ross Anderson, and Markus Kuhn.
• Directory of Books, Journals & Conferences on Digital Watermarking and Digital Watermarking Assessment Tools
• Slashdot article; - "Warezed SoundForge Files In Windows Media Player"
• Information hiding homepage
• Comparison of watermarking methods