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AlpVision SA
Rue du Clos 12
CH-1800 Vevey
Switzerland |
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T : +41 21 948 6464
F : +41 21 948 6465 |
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Digital Watermarking |
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Introduction: |
The AlpVision founders have significantly contributed to the scientific development of the Digital Watermarkin technology in the late 90's (see publications). To some extent one can consider that the current AlpVision proprietary digital security technology is a filiation of the Digital Watermarking scientific background, even though being extremely different by essence. See the Cryptoglyph page or the Fingerprint page to be convinced. |
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Digital Watermarking
is an adaptation of the commonly used
and well known paper watermarks to the
digital world. |
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Digital Watermarking basics: |
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Digital Watermarking describes methods and technologies that hide information, for example a number or text, in digital media, such as images, video or audio. The embedding takes place by manipulating the content of the digital data, which means the information is not embedded in the frame around the data. The hiding process has to be such that the modifications of the media are imperceptible. For images this means that the modifications of the pixel values have to be invisible. Furthermore, the watermark must be either robust or fragile, depending on the application. By "robust" we mean the capability of the watermark to resist manipulations of the media, such as lossy compression (where compressing data and then decompressing it retrieves data that may well be different from the original, but is close enough to be useful in some way), scaling, and cropping, just to enumerate some. In some cases the watermark may need to be fragile. "Fragile" means that the watermark should not resist tampering, or would resist only up to a certain, predetermined extent.
The example below shows that
digital watermarking allows hiding information
in a totally invisible manner. The original image is on the left; the
watermarked image is on the right and contains
the name of the author.
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What watermarking is used for?
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The first applications that came to mind were related to copyright protection of digital media. In the past duplicating art work was quite complicated and required a high level of expertise for the counterfeit to look like the original. However, in the digital world this is not true. Now it is possible for almost anyone to duplicate or manipulate digital data and not lose data quality. Similar to the process when artists creatively signed their paintings with a brush to claim copyrights, artists of today can watermark their work by hiding their name within the image. Hence, the embedded watermark permits identification of the owner of the work. It is clear that this concept is also applicable to other media such as digital video and audio. Currently the unauthorized distribution of digital audio over the Internet in the MP3 format is a big problem. In this scenario digital watermarking may be useful to set up controlled audio distribution and to provide efficient means for copyright protection, usually in collaboration with international registration bodies. |
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Are there any other applications where watermarking may be used?
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There are a number of possible applications for digital watermarking technologies and this number is increasing rapidly. For example, in the field of data security, watermarks may be used for certification, authentication, and conditional access. Certification is an important issue for official documents, such as identity cards or passports.
Example on the left of a protected identity card. The identity number "123456789" is written in clear text on the card and hidden as a digital watermark in the identity photo. Therefore switching or manipulating the identity photo will be detected |
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Digital watermarking permits linking information on documents. That means that key information is written twice on the document. For instance, the name of a passport owner is normally printed in clear text. But it would also be hidden as an invisible watermark in the passport photo. If anyone tries to tamper with the passport by replacing the photo it would be possible to detect the change by scanning the passport and verifying the name hidden in the photo.
The picture shows a printing machine
from Intercard for various types of
plastic cards (Courtesy of Intercard,
Switzerland). |
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Tampering with images: |
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Another application is the authentication of image content. The goal of this application is to detect any alterations and modifications in an image. The three pictures below illustrate this application. The picture on the left shows an original photo of a car that has been protected with a watermarking technology. In the center, the same picture is shown but with a small modification: the numbers on the license plate have been changed. The picture on the right shows the photo after running the digital watermark detection program on the tampered photo. The tampered areas are indicated in white. We can clearly see that the detected area corresponds to the modifications applied to the original photo. |
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Using digital watermarks for integrity
verification: the protected image is the image (a) above;
a modified image is obtained by swapping
the numbers 9 and 4 of the number plate (b); digital watermarking
technology allows detecting and highlights
the modified areas, as shown on
(c). |
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Invisible marking on blank paper: |
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Digital watermarks can also be adapted to mark white paper with the goal of authenticating the originator, verify the authenticity of the document content, or to date the document. Such applications are especially of interest for official documents, such as contracts. For example, the digital watermark can be used to embed the name of the lawyer or important information such as key monetary amounts. In the event of a dispute, the digital watermark is then read allowing authentication of key information in the contract.
AlpVision developed genuine process to invisibly mark white blank paper with normal and visible ink. This patented technology is now known as Cryptoglyph.
The image on the left shows blank paper marked by the invisible digital watermark using standard visible ink, with the Cryptoglyph technology. |
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Digital Media Management: |
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Beside applications in the fields of copyright
protection, authentication and security,
digital watermarks can also serve as invisible
labels and content links. For example,
photo development laboratories may insert
a watermark into the picture to link the
print to its negative. This way is very
simple to find the negative for a given
print. All one has to do is scan the print
and extracted the information about the
negative. In a completely different scenario
digital watermarks may be used as a geometrical
reference which may be useful for programs
such as optical character recognition
(OCR) software. The embedded calibration
watermark may improve the detection reliability
of the OCR software since it allows the
determination of translation, rotation,
and scaling. |
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Where is the technology heading in the future? |
An exhaustive list of digital watermarking applications is of course impossible. However, it is interesting to note the increasing interest in fragile watermarking technologies. Especially promising are applications related to copy protection of printed media. Examples here include the protection of bills with digital watermarks. Various companies have projects in this direction and it is very likely that fully functioning solutions will soon be available.
More scientific references are available
in our Publications list. |
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