Talking about the Concept and Application of Digital Watermarking Technology

【Abstract】This article starts with the concept of digital watermarking, introduces the basic characteristics, classification and application of digital watermarking technology, and puts forward some research trends of digital watermarking technology.
【Keywords】 digital watermarking; concealment; robustness

With the advent of the information age, especially the popularity of the Internet, the issue of information security has become increasingly prominent. Current information security technologies are basically based on cryptography theory. Whether traditional key systems or public key systems are used, the protection method is to control the access of files, that is, to encrypt files into ciphertext so that illegal users cannot Interpretation. However, with the rapid improvement of computer processing capabilities, this method of increasing the system secret level by increasing the key length has become increasingly insecure. On the other hand, multimedia technology has been widely used, and more and more audiovisual data are required for encryption, authentication, and copyright protection. Digital audiovisual data is essentially a digital signal. If this type of data is also encrypted using a password, its own signal properties are ignored. In recent years, many researchers have abandoned the traditional cryptography technology route, attempted to conceal and encrypt the audio-visual data with various signal processing methods, and used this technology to produce multimedia “digital watermarks”.

First, the digital era of seal - digital watermark

Digital Watermark technology refers to the use of signal processing methods to embed covert marks in digital multimedia data. Such marks are usually invisible and can only be extracted by a dedicated detector or reader. Digital watermarking is an important research direction of information hiding technology. The information embedded in a digital work must have the following basic characteristics to be called a digital watermark:

(A) The concealed watermarked data should not feel the difference compared to the original data. Embedding the watermarked data should not include the distortion that people can feel and cause the quality of the original data to decline. This is a subjective attribute and therefore there is no quantitative standard to measure.

(b) Robustness The so-called robustness refers to the fact that digital watermarks remain intact or can still be accurately identified after undergoing various unintentional or intentional signal processing procedures. Embedding the watermarked data is subject to some malicious processing of the data, such as filtering, requantization, jitter, etc., as well as some deliberate attacks, which should also be able to get embedded data.

(c) The uniqueness of the key means that different keys should not produce an equivalent watermark.

(d) Reliability of Detection The probability of watermark detection errors should be less than a suitable threshold. This feature describes the watermark detection algorithm must have a certain degree of certainty.

Second, the digital watermark classification

Digital watermarking techniques can be divided from different perspectives.

(a) According to the characteristics divided by the characteristics of the watermark digital watermark can be divided into two types of robust digital watermark and fragile digital watermark.

(b) Press the media attached to the watermark to divide the media attached to the watermark. We can divide the digital watermark into image watermarks, audio watermarks, video watermarks, text watermarks, and grid watermarks for three-dimensional mesh models.

(c) According to the detection process divided by watermark detection process can be divided into digital watermark watermark and blind watermark. The plaintext watermark requires raw data during the detection process, whereas the blind watermark detection requires only the key and does not require the original data.

(d) Divide the content by digital watermarking by content The watermark can be divided into meaningful watermarks and meaningless watermarks. Meaningful watermark means that the watermark itself is also the encoding of a digital image or digital audio segment; meaningless watermark only corresponds to a serial number.

(e) According to the purpose of use According to the use of watermarks, we can divide the digital watermark into bill anti-counterfeiting watermarks, copyright protection watermarks, tamper-prompt watermarks, and covertly-identified watermarks.

(6) According to the location of the hidden watermark, the hidden location of the digital watermark can be divided into time (empty) domain digital watermarking, frequency domain digital watermarking, time/frequency domain digital watermarking, and time/scale domain digital watermarking.

Third, the application of digital watermarking

The rapid development of multimedia technology and the popularity of the Internet have brought a series of political, economic, military, and cultural issues, and have produced many new research hotspots. The following issues that have caused widespread concern constitute the research background of digital watermarking.

(1) Intellectual property protection of digital works Copyright protection of digital works is currently a hot issue. Because copying and modification of digital works is very easy and can be done in the same way as the original works, the original creators have to adopt some methods that seriously damage the quality of the works to add copyright marks. Such obvious visible signs can easily be tampered with. "Digital watermarking" makes use of the principle of data hiding to make the copyright logo invisible or inaudible. It neither damages the original work nor achieves the purpose of copyright protection. However, realistically, digital watermarking products currently on the market are still technically immature and can easily be destroyed or cracked. There is still a long way to go before they are truly practical.

(II) Anti-counterfeiting of tickets in business transactions With the development of high-quality image input/output devices, especially the emergence of color inkjet, laser printers and high-precision color copiers with an accuracy of over 1200 dpi, the forgery of currency, cheques, and other bills has changed. It's easier. In addition, in the process of transformation from traditional business to e-commerce, there will be a large number of excessive electronic documents, such as scanned images of various paper documents. Even after the network security technology matures, various electronic tickets also need some non-cryptographic authentication methods. Digital watermarking technology can provide invisible certification marks for various bills, thus greatly increasing the difficulty of counterfeiting.

(3) The hidden identification of the audiovisual data and the identification information of the tampered data are often more confidential than the data itself. Data without identification information can sometimes not be used, but it is dangerous to mark this important information directly on the original document. The digital watermarking technology provides a way to hide the identification. The identification information is invisible on the original file and can only be read by a special reading program. This method has been adopted by some foreign remote sensing image databases. In addition, data tampering tips are also a very important task. The existing signal splicing and mosaicing technologies can be known as “sweeping and zapping”. Therefore, how to prevent tampering attacks on images, recordings, and video data is an important research topic. Digital watermark based tampering is an ideal technique to solve this problem. By hiding the state of the watermark, it can be judged whether the sound image signal has been tampered with.

(4) Covert communication and its countermeasures against digital watermarking not only provide a non-cryptographic secure way, but also trigger a revolution in information warfare, especially network intelligence warfare, resulting in a series of novel combat methods that have caused many National attention. The network intelligence warfare is an important part of information warfare. Its core content is the use of public networks for confidential data transmission. So far, academic research ideas in this area have not been able to break through the "document encryption" mode of thinking, however, encrypted files are often chaotic, easily attract the attention of the attacker. The widespread application of network multimedia technology makes it possible to use the public network for secure communication. With the use of digital audio and video signals, human beings can visually and auditorily monitor information and hide information in various time (empty) and transform domains. In order to achieve covert communications.

Fourth, the future of digital watermarking

Digital watermarking technology has many other uses, and its application area is still expanding. In addition to technological development, marketing and business planning are also extremely important and require in-depth analysis and strategic planning. Technology promotion and popularization are also essential to ensure that the market is ready to accept digital watermarking technology. Give some ideas for this.

First, how to use the watermark algorithm to solve the multimedia information security problem in the network environment has become a current research hotspot. The security issues of multimedia information are: security transfer, access control and copyright protection. The first two purposes can be achieved through encryption and decryption. However, the decrypted data can be freely distributed and transmitted on the network. Embed a unique mark (ie, digital watermark) in digital content. When a dispute arises, based on the proposed watermark, you can prove the true owner of the copyright, or identify the person who spread it illegally. However, these applications are only passively reflected in the dispute, and due to the lack of corresponding legal support, these ideas have not been implemented. Therefore, it has been proposed that digital watermarking agents use mobile agent technology to automatically search for illegal or unauthorized digital media content on the network. However, the premise is that the host computer needs to install a corresponding agent program, which brings new security issues. We propose to add a watermark detection algorithm (digital watermarking agent) to the routers on the network communication path to detect illegal transmissions on the network, thereby eliminating the illegal transmission of digital media content on the network.

Second, some people have already proposed a scheme for embedding a watermark under a multicast system. However, the specific characteristics of the watermarks that need to be satisfied under this scheme have not been examined in detail. The traditional multicast based on the Internet first needs to study the characteristics of the watermarking algorithm under the multicast system, and then design the corresponding watermarking algorithm for the characteristics.

Third, the construction of digital cinema requires the use of digital watermark protection, by embedding different versions of the watermark, to track illegal leaks. Among them, for small-scale applications, as long as the embedded robust watermark, it can meet the requirements. For large-scale applications, collusion attacks are mainly considered. In addition, the architecture of the digital cinema must also be combined. If multicast is used, the network characteristics and compression coding must be combined.

Fourth, propose the concept of active watermark. First, different levels of watermarks are embedded in the media to determine the user's rights. The watermarks are detected in the network. The router determines whether to forward them according to the permissions of these watermarks, and provides detailed reports of the interception. Secondly, the watermark module is embedded in the firewall, the outgoing media content is extracted, the watermark is extracted, and it is judged whether the content is important according to the watermark, and cannot be leaked out, and the multimedia content of the local area network can be effectively protected; the multimedia content passed in can be extracted according to The watermark determines whether the employee has the right to use it, thus preventing unnecessary illegal infringement.

Wang Zhenduo, Li Jie (Department of Computer Science, Beihua Institute of Aerospace Technology

Reprinted from: Popular Science and Technology Magazine