The emergence of the Internet has profoundly affected many spheres of human life. Thanks to advances in telecommunications, it is now possible to stay connected to the Internet around the clock, and share experiences with other users in real-time. Many services have been established to help exactly that cause, and they commonly come in the form of social networks. The abundance of content publicly available via these networks motivated researchers to devise new methods for its analysis and extraction of patterns and knowledge hidden in it. Data mining, as a way of automatic - or more commonly semi-automatic - process of extraction of information, patterns, trends, rules and knowledge from large datasets, plays a particularly important role in those efforts. The work presented in this book explores the possibility of using large amounts of publicly available user-generated multimedia content to discover new knowledge and devise more efficient solutions to several existing problems, such as video quality assessment (VQA) algorithms improvement and human mobility analysis.