1. Introduction

Social networks have undergone a dramatic growth in recent years. Such networks provide an extremely suitable space to instantly share multimedia information between individuals and their neighbours in the social graph. Social networks provide a powerful reflection of the structure, the dynamics of the society and the interaction of the Internet generation with both people and technology. Indeed, the dramatic growth of social multimedia and user generated content is revolutionizing all phases of the content value chain including production, processing, distribution and consumption. It also originated and brought to the multimedia sector a new underestimated and now critical aspect of science and technology, which is social interaction and networking. The importance of this new rapidly evolving research field is clearly evidenced by the many associated emerging technologies and applications, including (a) online content sharing services and communities, (b) multimedia communication over the Internet, (c) social multimedia search, (d) interactive services and entertainment, (e) health care and (f) security applications. It has generated a new research area called social multimedia computing, in which well-established computing and multimedia networking technologies are brought together with emerging social media research.