What is watermark technology?

Watermarking technology, in short, is a technique that embeds specific information (such as text, identification, serial numbers, etc.) into a medium (such as images, audio, video, documents, etc.) in an invisible or almost invisible manner. These pieces of information can exist as copyright identifiers, identity verifications, or tracking clues without affecting the normal use of the carrier. The core of watermark technology lies in its concealment, robustness, and security, that is, watermark information should be difficult to detect, tamper with, or remove, and able to resist certain signal processing operations.
Classification of Watermark Technology
Watermark technology can be roughly divided into the following categories based on its characteristics and application purposes:
Visible watermark and invisible watermark
Visible watermark: directly embedded in a visible form into the carrier, such as text or icons on an image. This type of watermark is mainly used for copyright declaration or advertising promotion, but may have a certain impact on the aesthetic value of the carrier.
Invisible watermark: Embedding information into the pixels, frequency, or transform domain of the carrier through a specific algorithm, making the watermark information visually invisible. Invisible watermarking is the main means of copyright protection and identity verification.
Robust watermark and fragile watermark
Robust watermark: A watermark designed to resist various signal processing operations such as compression, filtering, cropping, etc. This type of watermark can maintain detectability even after certain modifications to the carrier content, making it suitable for copyright protection and tracking.
Fragile watermark: A watermark that is highly sensitive to any minor changes to the content of the carrier. Fragile watermarking is mainly used for integrity verification, such as detecting whether an image or audio file has been tampered with.
Spatial domain watermarking and transform domain watermarking
Spatial domain watermarking: Directly embedding watermark information in the pixel space of the carrier. This method is simple to implement, but its robustness is relatively weak.
Transform domain watermarking: Using mathematical transformations such as Discrete Cosine Transform (DCT) and Discrete Wavelet Transform (DWT) to embed watermark information in the transform domain. Transform domain watermarking usually has better robustness and concealment.
The working principle of watermarking technology
The working principle of watermarking technology involves three main steps: information encoding, embedding, and detection:
Information encoding: Convert the information to be embedded (such as copyright information, serial numbers, etc.) into a format suitable for embedding. This usually includes processes such as encryption, encoding, and modulation of information.
Embedding process: Using specific algorithms and keys, the encoded information is embedded into the appropriate location on the carrier. The embedding process needs to ensure that the watermark information is visually invisible or almost invisible, and minimize the impact on the quality of the carrier.
Detection process: When it is necessary to verify copyright, trace the source, or detect tampering, watermark information is extracted from the carrier through corresponding detection algorithms. The detection process may involve preprocessing of the carrier, transform domain analysis, and information decoding.
Application Fields of Watermark Technology
Watermark technology has been widely applied in multiple fields, including:
Copyright protection: Embedding copyright information in digital media such as images, audio, and video to prevent unauthorized copying and dissemination.
Identity verification: Embedding user identity information into documents, certificates, and other carriers to verify the authenticity of identity.
Data tracking: Embedding serial numbers or tracking codes on product packaging, labels, etc. to achieve full process tracking and anti-counterfeiting of products.
Integrity verification: Using fragile watermarking technology to detect whether images, audio and other files have been tampered with, ensuring the integrity and authenticity of the data.
Military and National Security: Applying watermark technology in military communication, intelligence transmission, and other fields to improve the concealment and security of information.