What is digital watermarking?
Principle of digital watermarks
General features required for digital watermarks
Materials suitable for watermarking
Structure of a digital watermark
Digital watermarking is a technology for embedding various
types of information in digital content. In general, information
for protecting copyrights and proving the validity of data
is embedded as a watermark.
Why do we need to embed such information in digital content
using digital watermark technology? The Internet boom is
one of the reasons. It has become easy to connect to the
Internet from home computers and obtain or provide various
information using the World Wide Web (WWW).
All the information handled on the Internet is provided
as digital content. Such digital content can be easily copied
in a way that makes the new file indistinguishable from
the original. Then the content can be reproduced in
large quantities.
For example, if paper bank notes or stock certificates
could be easily copied and used, trust in their authenticity
would greatly be reduced, resulting in a big loss. To prevent
this, currencies and stock certificates contain watermarks.
These watermarks are one of the methods for preventing counterfeit
and illegal use.
Digital watermarks apply a similar method to digital content.
Watermarked content can prove its origin, thereby protecting
copyright. A watermark also discourages piracy by silently
and psychologically deterring criminals from making illegal
copies.
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A watermark on a bank note has a different transparency
than the rest of the note when a light is shined on it.
However, this method is useless in the digital world.
Currently there are various techniques for embedding digital
watermarks. Basically, they all digitally write desired
information directly onto images or audio data in such a
manner that the images or audio data are not damaged. Embedding
a watermark should not result in a significant increase
or reduction in the original data.
Digital watermarks are added to images or audio data in
such a way that they are invisible or inaudible Ñ unidentifiable
by human eye or ear. Furthermore, they can be embedded in
content with a variety of file formats. Digital watermarking
is the content protection method for the multimedia era.
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1. Elements of digital content can be directly manipulated
and information can be embedded in them.
2.Deterioration of the quality of digital content is minimized.
3.Watermarks are retained and detectable after the digital
content is edited, compressed, or converted.
4.The structure of a watermark makes it difficult to detect
or overwrite (alter) the embedded information (watermark
contents).
5.Processing required for watermarking and detection is
simple.
6.Embedded watermark information cannot be eliminated without
diminishing the quality of the digital content that carries
the watermark.
7.The watermark information embedded in digital content
can be detected as required.
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Digital watermarking is applicable to any type of digital
content, including still images, animation, and audio data.
It is easy to embed watermarks in material that has a comparatively
high redundancy level ("wasted"), such as color still images,
animation, and audio data; however, it is difficult to embed
watermarks in material with a low redundancy level, such
as black-and-white still images.
To solve this problem, we developed a technique for embedding
digital watermarks in black-and-white still images and a
software application that can effectively embed and detect
digital watermarks.
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The structure of a digital watermark is shown in the following
figures.
The material that contains a digital watermark is called
a carrier. A digital watermark is not provided as a separate
file or a link. It is information that is directly embedded
in the carrier file. Therefore, the digital watermark cannot
be identified by simply viewing the carrier image containing
it. Special software is needed to embed and detect such
digital watermarks. Kowa 's SteganoSign is one of these
software packages.
Both images and audio data can carry watermarks. A digital
watermark can be detected as shown in the following illustration.
Still in its infancy, digital watermark technology will
continue to be improved. Kowa will always maintain a leadership
role by actively developing and introducing the latest and
the best digital watermark technology in the industry.
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