## 1 Introduction  
Intensive development of techniques for 3D modeling and 3D digitization of cultural heritage (movable and immovable), such as photogrammetry [1], has led to the issue of protection and rights to take over the obtained 3D models. Although the problem of data protection against theft and misuse of various other types of digital information (software, software code, audio, and video files) has previously been solved [2], few solutions have been created to protect 3D models. The growing use of 3D digitization of cultural heritage objects, which has flourished in recent years, has significantly increased the need to protect 3D models. More and more cultural institutions use the mentioned modern methods of 3D digitalization to create high-quality, realistic 3D models of objects of historical significance. More and more projects financed/supported by the state, cultural institutions, and the competent ministry are based on the digitization of cultural heritage and the creation of digital libraries and archives [3, 4, 5]. Moreover, the creation of virtual museums [6] and virtual presentations of cultural heritage, which use innovative technologies such as virtual and augmented reality, is becoming increasingly popular [7]. The 3D models created by digitization of objects within such projects are the heritage of the cultural institutions and countries, and the contract allows the distribution of the obtained 3D models to a certain group of people (mostly employees of cultural institutions or scientists) for non-commercial use. Although the majority of the population would like 3D models to be widely available to be used for various, even commercial purposes, 3D models of objects of cultural significance can be abused if they are distributed without protection. The fear of copying their work and stealing ideas (based on 3D models) is also present among the curators. The term abuse refers to the download of 3D digital models from the Internet and their distribution by users who present someone else's work as their own. One of the standard ways to protect digital content is licensing, in the case of software or music sharing, but in the case of the 3D virtual models, cryptography is the solution [8]. In modern times, the dominant way of protecting an artwork is the watermark. The digital preservation policies in most cultural heritage institutions are not developed and the created archives are technologically obsolete [9]. A bridge between physical engineering and cyber-crime is 3D printing because digital contents created or stolen in one country or institution can be transported around the world via the Internet to be physically created. In many countries, the laws are too primitive to cover similar types of cyber-crime [10]. Digital archives and digital cultural heritage contents require special skills to manage the copyrights and intellectual properties. The relationship between intellectual property and digitization has not been fully legally regulated [11]. The process of protection of intellectual property rights requires consideration of issues relating to the balance between fair conditions for access to cultural heritage objects for digitization and modern media for presentation [12]. In addition to the issue of intellectual property in the digitization of objects of cultural significance and their presentation, it is necessary to take into account ethical principles and issues [13]. Despite the growing need for protection against the misuse of digital 3D models of cultural heritage, little research addresses this issue. Watermarks are described as structures containing information that is embedded into objects so that they do not interfere with the intended use [14]. The authors presented fundamental techniques and algorithms for embedding data into the geometry of 3D models. They noted three requirements that are common to a majority of applications: watermarks must be unnoticeable, robust, and space efficient.