The field of data hiding in the context of digital technology is quite young. Although the first paper on electronic data embedding can be traced back to a patent application issued in 1954, the active research in this field began only in the early nineties. The following years have witnessed an exponential increase in the volume of published articles and patents. By now, steganography and digital watermarking have been established as stand-alone fields with their dedicated regular

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... gatherings. The first applications, that have driven the research effort in the early beginnings, focused on copyright protection of multimedia data exchanged in digital form. Research was mainly oriented towards robust watermarking, that is, the insertion within to-be-protected digital product of an imperceptible code bearing some information about the product itself, that is, the product owner, its allowed uses, or the buyer's ID for tracing purposes. These applications have spawned a plethora of problems ranging from secure protocols, design of supporting infrastructure, to an intense research on security and development of attacks. As the research continued, it has become evident that many other application scenarios exist where data hiding could be applied successfully. Fragile watermarks were proposed for detection of malicious and inadvertent manipulations and for authentication purposes. Steganography, or covert communication, saw the first attempts to formalize the concept of steganographic security and prove strengths as well as weaknesses of proposed supposedly secure covert schemes. Other commercial applications, such as broadcast monitoring, digital cinema, image and video captioning, audio-in-video embedding for multilanguage broadcasting, image and video indexing, transmission error recovery and concealment, and others have generated rapidly increasing interest among industrial and academic researchers. The field of data hiding has also certain special appeal so typical of every newly emerging area-it is pristine and largely unexplored. If the applications and concepts could be compared to apple trees and the problems to their fruits, one could say that there are still a number of trees that were not visited bearing large, juicy apples, with a few pieces hanging quite low. Some trees have been visited so many times that one needs a long ladder to get to new fruits. The goal of this special issue is to reveal the existence of new trees or as yet unvisited branches of existing trees, presenting to you the fruit-new results and insights, thus paving the way for future developments in the field and for a better understanding of its potential in today's world. The special issue starts with a review on the history, present, and future of applications of data hiding written by Cox and Miller. The authors ask provocative questions about the future fate of data hiding while giving examples of practical applications. In their view, the application that gave birth to the recent research activity-the copyright protection-is giving way to other technologies, such as broadcast monitoring, authentication, and tracking content distributed within corporations. According to Cox and Miller, while considerable progress has been made toward enabling these applications-perceptual modeling, security threats and countermeasures, and the development of a bag of tricks for efficient implementations-further progress is needed in methods for handling geometric and temporal distortions. The paper has a very extensive bibliography, which