Vízjel

Vízjel is a watermark, the mark embedded in paper or digital media to indicate origin, ownership, or authenticity. The word derives from víz, meaning water, and jel, meaning sign. In physical papermaking, a watermark is created by varying the paper’s density or thickness during production, typically through the design of a mold or the arrangement of wire in the papermaking process. When held up to light, the watermark becomes visible. Watermarks have a long history as security features for currency, official documents, and fine papers, because they are difficult to counterfeit and can be used to verify provenance.

Digital vízjel – digital watermarking – embeds information into digital media such as images, audio, or video without markedly affecting perceptible quality. The embedded data can identify authorship, track distribution, or verify integrity. Watermarks are categorized as fragile, which are destroyed by modification, or robust, designed to withstand common transformations. Techniques include spatial-domain methods that alter pixel values and frequency-domain methods that embed data in transformed representations.

Applications and considerations include currency security, government and legal documents, stamps and certificates, branding and copyright protection in photography and publishing, and monitoring of media distribution. Digital watermarking intersects with rights management, forensic analysis, and privacy concerns, and the field continues to evolve with advances in processing power, machine learning, and cryptography.