Disclosed herein are methods, systems, and apparatus, including computer programs encoded on computer storage media, for hiding copyright information in printable materials. One of the methods includes generating, by a computing device, a unique identifier (ID) based on copyright information associated with digital content, wherein the copyright information and the digital content are recorded on a blockchain of a blockchain network; determining one or more features associated with one or more printable materials; and converting the unique ID to a digital watermark based on the one or more features, the digital watermark not being apparent to an unaided human eye when printed on the one or more printable materials and enabling retrieval of the copyright information from the blockchain based on the unique ID.
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