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A watermark is a design made by impressing a water coated metal stamp or roll onto paper during manufacturing. The result is a pale shadowy image that is clearly visible when the paper is held up to the light. Watermarks originally were used to identify paper manufacturers. They were introduced into modern Europe in Italy in 1282. They have also been used on postage stamps, currency and other government documents to prevent counterfeiting.

Encoding an identifying code into digitized music, video, picture, or other file is known as a digital watermark.