Understand digital watermarking technology

Digital watermarking technology is the latest international information hiding technology. The so-called digital watermarking technology is to embed copyright information such as numbers, serial numbers, text, image logos, etc. into multimedia data so as to play a role of copyright tracking and copyright protection. In addition, digital watermarking has important application value in authentication, covert communications, logo implied, and electronic identity authentication. The research of digital watermarking technology involves the research fields of informatics, cryptography, mathematics, computer science, pattern recognition and other subjects, making the hidden information more covert and safe, and also has symmetry and correctability. Research indicates that digital watermarking has a huge and broad application prospects, and has attracted extensive attention from the academic community, industry, and the military.

In order to identify the authenticity of banknotes in daily life, people usually point the banknotes to the light source, and they will find that there are clear image information in the real banknotes. This is the watermark we are familiar with. The reason why the watermarking technique is adopted is because the watermark has its unique property: the first watermark is an almost invisible imprint, which must be placed in a specific environment to be seen without affecting the use of the article; the second watermark is produced and copied. It is more complicated, requires special processes and materials, and the watermark on the print is difficult to remove. Therefore, watermarks are often used in important publications such as cheques, certificates, passports, and invoices. An important means of judging the authenticity of printed matter for a long time is to check whether it contains watermarks.

With the advent of the digital age, the multimedia digital world is full of diversity. Digital products affect almost everyone’s daily life. How to protect these digital products that are closely related to us, such as copyright protection, information security, data authentication, access control, etc., are increasingly valued and urgently needed. Referring to the meaning and function of ordinary watermarks, people adopt similar concepts to protect multimedia data such as digital images and digital music, thus resulting in the concept of “digital watermarking”. The so-called "digital watermarking" is the addition of certain digital information to the multimedia data, such as adding the information of the maker in the digital photo, adding the information of the movie company in the digital video disc, and the like. Similar to the characteristics of ordinary watermarks, digital watermarks are almost invisible in multimedia data (such as digital photos) and are difficult to be destroyed. Therefore, digital watermarking has great potential in today's computer and Internet era.

What digital watermarks can do

The concept and method of digital watermark was first proposed to protect the copyright of multimedia data. With the development of computers and the Internet, more and more artworks, inventions or ideas have begun to be expressed in the form of multimedia data, such as photography with a digital camera, watching a movie with a digital cinema, listening to music with an MP3 player, and drawing with a computer. Paintings and so on. The multimedia data involved in all activities contains a lot of valuable information. Compromising, forging, copying, and illegally publishing original works have become a breeze in the information age compared to the hard work of authors in creating these multimedia data. Anyone can easily create a copy of the multimedia data. Compared with the original data, the copied multimedia data will not have any quality loss, that is, it can completely "clone" the multimedia data. Therefore, how to protect the "intellectual property rights" attached to these data is an urgent problem to be solved. Digital watermarking is just an effective means to solve this kind of "copyright problem." For example, the former painter used the seal or the signature to identify the author of the work. Today, he can add his own name to the work through the digital watermark to complete the identification of the copyright. Similarly, audiovisual companies can also add information such as company names and logos to published tapes and CDs. This protects the copyright of multimedia data by tracking the digital watermark information in the multimedia data.

In addition to its application in copyright protection, digital watermarking technology is also very useful in the authentication of documents (prints, electronic documents, etc.). For example, in the case of red-headed documents issued by government agencies, the traditional method of document authentication is to identify papers for documents. Whether the seal or seal complies with the specifications and standards, the disadvantage is that it is easy to be forged regardless of whether the paper, seal or stamp is stamped. In particular, the seal, although the government departments have strict regulations on the management and production of the seal, there is still the so-called "a radish carved a chapter" in the society. This shows that the traditional method is extremely imperfect. The use of digital watermarking technology can effectively solve this problem. With digital watermarking as an information carrier, adding certain information to the red-head file makes the file not only have seals or stamps, but also has intangible digital watermark information, thereby greatly increasing the difficulty of file forgery. Adding digital watermark information to a document also means that some information can be written twice in the document. For example, the passport holder’s name is clearly printed in the passport, and can also be hidden as a digital watermark in the portrait. If someone wants to forge a passport by replacing the portrait, it may be detected by scanning the passport. The watermark information in the avatar does not match the name printed on the passport, and the forged passport is found.

In addition digital watermarking is also used for multimedia data access control and copy control. For example, secret digital watermark information in a CD data disc can conditionally control what kind of person can access the content in the CD disc. At present, DVDs have been hot in the domestic electronics market. Many large companies have begun to study how to apply digital watermarking systems to improve DVD access and copy control. For example, it is hoped that the DVD player in the consumer's hands will allow unlimited copying of home videos or expired TV programs. The digital watermark added to the home video does not contain any control logo. The digital watermark in the TV program is identified as "copy once", " Duplicate many times, and the commercial video program is marked as "not allowed to copy", and the relevant playback device will discriminate these digital watermarks and play a corresponding role. This not only guarantees the freedom for consumers to privately copy and exchange programs, but also effectively controls commercial infringements. At present, all the solutions have been formed. The problem is that the security, effectiveness, and simplicity of the solution need to be further tested and cannot be provided to DVD manufacturers and users for the time being.

Digital watermarking technology can also be applied to the secure communication of information. Because it is difficult for people to perceive the existence of digital watermark information in multimedia data, some important information can be hidden in ordinary multimedia data during the transmission process, thereby avoiding third party eavesdropping and monitoring. Foreign newspapers reported that terrorist leader Bin Laden used publicly released digital watermarking technology to hide Al Qaeda directives from digital watermarks in ordinary digital photos and then posted them on BBSs of some websites. The rules extract digital watermark information from digital photos. This approach is more covert than ordinary telephone communications, e-mail communications, and encrypted communications. It is not easy to monitor and is difficult to detect.