Modern telecommunication systems have seen an increased demand on delivering new types of digital media such as extended reality. The currently rolled out fifth generation mobile networks are expected to support virtual reality, augmented reality, and other immersive media. On the other hand, securing communication to prevent access from adversaries and hiding secret information have become an integral part of digital communications. In particular, steganography is a class of data hiding that provides covert communication between two parties such that the information exchange cannot be observed by an attacker. Because the human auditory system and human visual system are relatively insensitive to small changes in digital media, hiding secret information in digital media has increasingly been used. This thesis focuses on data hiding in 360^o videos which offer large resolutions that can be used for hiding secret data. To keep the computational load of data hiding low, least significant bit (LSB) data hiding methods are considered and their performance is assessed in terms of capacity and imperceptibility. The proposed LSB data hiding methods account for the human viewing behavior of watching 360^o videos on head-mounted displays (HMDs).

This thesis is divided into an introduction part and a research part based on four peer-reviewed publications. The introduction provides fundamentals of data hiding, terminologies used in data hiding, LSB data hiding concepts, and performance measures used to assess data hiding methods. The first paper in the research part provides a survey on LSB data hiding in digital audio, images, videos, and three-dimensional (3D) media. The survey shows the tremendous potential of LSB data hiding in digital media and may assist in developing novel applications based on suitable performance trade-offs between data hiding attributes. It also reveals that LSB data hiding in 3D media such as 360^o videos is not as developed as for conventional digital media. The second paper proposes an LSB data hiding method for 360^o videos which takes into account that humans pay more attention to the equator region compared to the poles when viewing 360^o videos on an HMD. The third paper presents a novel viewing direction based LSB data hiding method for 360^o videos. The distributions of viewing direction frequency for latitude and longitude are used to control the amount of secret data to be hidden at the latitude, longitude, or both latitude and longitude of 360^o  videos. Analytical expressions for the capacity offered by this method are derived and imperceptibility is assessed through fidelity and quality metrics. The fourth paper proposes a viewing direction weighted bit plane LSB data hiding method for 360^o videos that uses normalized Gaussian mixture models to control the amount of secret data and the number of bit planes used for data hiding in the latitude and longitude.