Concept

Watermark

Summary
A watermark is an identifying image or pattern in paper that appears as various shades of lightness/darkness when viewed by transmitted light (or when viewed by reflected light, atop a dark background), caused by thickness or density variations in the paper. Watermarks have been used on postage stamps, currency, and other government documents to discourage counterfeiting. There are two main ways of producing watermarks in paper; the dandy roll process, and the more complex cylinder mould process. Watermarks vary greatly in their visibility; while some are obvious on casual inspection, others require some study to pick out. Various aids have been developed, such as watermark fluid that wets the paper without damaging it. A watermark is very useful in the examination of paper because it can be used for dating documents and artworks, identifying sizes, mill trademarks and locations, and determining the quality of a sheet of paper. The word is also used for digital practices that share similarities with physical watermarks. In one case, overprint on computer-printed output may be used to identify output from an unlicensed trial version of a program. In another instance, identifying codes can be encoded as a digital watermark for a music, video, picture, or other . Watermarks were first introduced in Fabriano, Italy, in 1282. At the time, watermarks were created by changing the thickness of paper during a stage in the manufacturing process when it was still wet. Traditionally, a watermark was made by impressing a water-coated metal stamp onto the paper during manufacturing. The invention of the dandy roll in 1826 by John Marshall revolutionised the watermark process and made it easier for producers to watermark their paper. The dandy roll is a light roller covered by material similar to window screen that is embossed with a pattern. Faint lines are made by laid wires that run parallel to the axis of the dandy roll, and the bold lines are made by chain wires that run around the circumference to secure the laid wires to the roll from the outside.
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Related courses (1)
EE-552: Media security
This course provides attendees with theoretical and practical issues in media security. In addition to lectures by the professor, the course includes laboratory sessions, a mini-project, and a mid-ter
Related publications (3)

Objective Evaluation of the Perceptual Quality of 3D Watermarking

Touradj Ebrahimi, Elisa Drelie Gelasca

In this paper an objective metric to measure the perceptual quality of watermarked 3D meshes is presented. The metric, which is based on a black-box approach, relies on the measurement of the roughness of 3D meshes before and after the insertion of the wat ...
IEEE2005

Toward perceptual metrics for video watermark evaluation.

Touradj Ebrahimi, Elisa Drelie Gelasca

Assessing and comparing the performance of watermarking algorithms is di cult.The visibility of the watermark is an important aspect in this process.In this paper,we propose two metrics for evaluating the visual impact of video watermarks.Based on several ...
SPIE2003

Perceptual Quality Assessment for Video Watermarking

Touradj Ebrahimi, Elisa Drelie Gelasca

The reliable evaluation of the performance of watermarking algorithms is difficult. An important aspect in this process is the assessment of the visibility of the watermark. In this paper, we address this issue and propose a methodology for evaluating the ...
EUSIPCO2002
Related concepts (2)
Paper
Paper is a thin sheet material produced by mechanically or chemically processing cellulose fibres derived from wood, rags, grasses, or other vegetable sources in water, draining the water through a fine mesh leaving the fibre evenly distributed on the surface, followed by pressing and drying. Although paper was originally made in single sheets by hand, almost all is now made on large machines—some making reels 10 metres wide, running at 2,000 metres per minute and up to 600,000 tonnes a year.
Banknote
A banknote—also called a bill (North American English), paper money, or simply a note—is a type of negotiable promissory note, made by a bank or other licensed authority, payable to the bearer on demand. Banknotes were originally issued by commercial banks, which were legally required to redeem the notes for legal tender (usually gold or silver coin) when presented to the chief cashier of the originating bank. These commercial banknotes only traded at face value in the market served by the issuing bank.