Vatnsmerki

Vatnsmerki, in Icelandic usage, refers to a watermark. A watermark is a mark or pattern embedded in a material or media that becomes visible when light passes through it or is detected by appropriate tools. Watermarks are used to indicate authenticity, origin, or copyright, and they can be visible or invisible to the casual viewer.

In traditional papermaking, a watermark is created by shaping the sheet during the wet end, typically by using a raised design in the papermaking mold or rolling. The result is a pattern that appears lighter or darker when the sheet is held up to light. Watermarks have a long history, with notable use in European paper mills dating to the 13th to 14th centuries. They are common on security papers, archival documents, and many banknotes, serving as a quick visual or tactile indicator of legitimacy.

Digital watermarks, or digital watermarking, extend the concept to electronic media. They embed information into digital content (images, audio, video) so ownership, provenance, or usage rights can be detected even after common processing. Watermarks can be visible (overlaid logos or text) or invisible (hidden data embedded in the signal). Techniques vary, including spatial-domain methods and frequency-domain methods (such as transforms), and resilient schemes are designed to survive compression, resizing, or cropping.

Applications cover currency and official documents, product and brand protection, photography and media distribution, and forensic or copyright tracking. Limitations include potential quality impact, the possibility of removing or tampering with marks, and trade-offs between visibility, robustness, and imperceptibility. See also watermarking and security printing.