When speaking of digital data, a watermark is a type of information that is "hidden" among the data. This is mostly used with pictures and sound data.

Watermarks serve mostly only to identify the picture or sound; The artist can assign any watermark to a picture, containing (say) his name and your customer number, so that if someone copies the picture from you, he knows you leaked it. (Most of the image watermarks only record the artist, but sound watermarks such as SDMI record also the recipient. Caveat emptor.)

Unfortunately, watermarks are as of yet not a good way to put information into data; mostly for two reasons:

  • None of the watermark algorithms can withstand tampering. Change image shades a bit, *poof* goes the watermark. Crop the image, *poof* goes the watermark. Save in lossy format - *bang*, now you killed it dead! And so on. (For more proof of this, see the results of "stirmark" research.)
  • Watermarks tend to lower signal quality (or make pictures look worse). Sometimes, the watermarks are very audible or visible!

See also steganography.

Watermarks are designs imprinted into paper with wires in the mould. Intentional watermarks have been imprinted into paper dating as early back as the Byzantine era in Greek civilization. The markings seen largely consist of simple designs focused around nature such as trees and flowers.

The European guilds and tradesmen around the year 1282 were the first group to mass-produce paper with watermarks as an indication of the paper’s quality and craftsmanship. In 1848, WH Smith created the watermark technology that enabled a marking to be printed in both light and dark shades, allowing the creation of complex and intricate pictures, such as portraits.

Watermarks come in several degrees of complexity from simple letters or designs to elaborate portraits of monarchs and noblemen. They have even been created in three dimensions on paper using leaves and solid moldings. In modern times, watermarks are used both as a decoration on stationary, as well as a security system to prove the authenticity of documents such as checks and paper money.

Wa"ter*mark` (?), n.

1.

A mark indicating the height to which water has risen, or at which it has stood; the usual limit of high or low water.

2.

A letter, device, or the like, wrought into paper during the process of manufacture.

"The watermark in paper is produced by bending the wires of the mold, or by wires bent into the shape of the required letter or device, and sewed to the surface of the mold; -- it has the effect of making the paper thinner in places. The old makers employed watermarks of an eccentric kind. Those of Caxton and other early printers were an oxhead and star, a collared dog's head, a crown, a shield, a jug, etc. A fool's cap and bells, employed as a watermark, gave the name to foolscap paper; a postman's horn, such as was formerly in use, gave the name to post paper."

Tomlinson.

3. Naut.

See Water line, 2.

[R.]

 

© Webster 1913.

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