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Top1. Introduction
Digital information revolution has numerous advantages with new challenges and opportunities for innovation. The three-dimensional (3D) meshes are relatively new kind of media that achieves a growing success, where their applications are widely transferred through the Internet. It has extensive applications in various domains, such as in entertainment industry (e.g. film, video games, virtual reality), and in technical/scientific applications (e.g. medical images that aid in the diagnosis, computer-assisted surgery, remote industrial objects design, physical simulations, cartography, geology, astronomy). A 3D mesh is a polygonal facets collection that consists of three main elements, namely the vertices, edges and facets. It provides a real 3D object appropriate approximation (Wang et al., 2008). The 3D mesh can be described using: 1) geometry information that represent the coordinates of all its vertices, and 2) the connectivity information that offers the adjacency relations between the elements. Additionally, it is fairly easy to convert the different representations to low-level effective 3D mesh model.
The increased use of multimedia applications poses growing problems concerning the protection of copyright and illegal use of controlled 3D meshes. Moreover, wireless networks and internet offer pervasive channels for information exchanging, which necessitates security and privacy issues. In the digital domain, ease editing and impeccable reproduction allow the ownership protection and the unauthorized tampering prevention of the transmitted data using developed data hiding techniques. Consequently, digital watermarking and data hiding schemes achieve extensive evolution in recent years and attract the researches attention. Such schemes have been involved for various applications, such as access control, ownership protection, copyright protection and authentication purposes (Dey et al., 2012a; 2012b; Dey et al., 2013a; Biswas et al., 2013). Robustness against compression, imperceptibility, and hiding many bits are the elementary requirements for multimedia data hiding applications.
In order to identify the content owner, watermarking is considered to be one of the effective solutions that involve watermark inserting/hiding some secret information in the cover content. This guarantees reliable authenticity protection of the multimedia data by inserting information in the data itself. The 3D models creation requires intensive resources in terms of time and cost. These models have a scientific and commercial value; however, their illegal use may lead to loss of time, money and effort. In order to avoid these factors, the robust watermark can be carried out. Previously, watermarking technologies were applied to traditional media data, such as image, digital audio, and video. Recently, 3D polygonal meshes have been widely used in many fields that need realistic visualization of the object (Ali, 2012). Since, watermarking schemes that has been emerged for audio, image, and video is challenging to adapt for 3D geometric models. Thus, only few watermarking methods have been proposed for 3D geometric models in relation to other media.
Robust watermark embedding to a specified 3D models guarantees security and protection of these precious objects. The information inserted can be used to enforce copyright, comments, detect tampering, or identify legitimate data buyers.
Recently, due to the rapid growth of computer graphics and acquisition technology, employing 3D information for modeling and representing real world scenes has become common in many applications (El-Bendary, 2012). Typically, mesh watermarking refers to the insertion of information into 3D models in a persistent and imperceptible way (Ben Amar et al., 2012; Abderrahim et al., 2013; Wang et al., 2008; Cho et al., 2007; Salehpoor & Behrad, 2012). These techniques are more difficult compared to image watermarking due to the increased complexity associated with meshes in arbitrary shapes and the existence of many insoluble attacks (Dey et al., 2012c, Dey et al., 2013b; Dey et al., 2013c)