The notion of context plays a significant role in multimedia content search and retrieval systems. In this paper we focus our research efforts on a visual context knowledge representation, to be utilized for multimedia high-level concept detection. We propose and describe in detail types of contextual relations evident within the multimedia content, model them and provide a clear methodology on how to extract them. A visual context ontology is introduced, containing relations among different types of content entities, such as images, regions, region types and high-level concepts. In this manner, we facilitate traditional object detection approaches towards semantical interpretation. The application of the proposed knowledge structure provides encouraging initial results, improving the efficacy of related multimedia analysis techniques.