Human-centered implicit tagging: Overview and perspectives

Tags are an effective form of metadata which help users to locate and browse multimedia content of interest. Tags can be generated by users (user-generated explicit tags), automatically from the content (content-based tags), or assigned automatically based on non-verbal behavioral reactions of users to multimedia content (implicit human-centered tags). This paper discusses the definition and applications of implicit human-centered tagging. Implicit tagging is an effortless process by which content is tagged based on users' spontaneous reactions. It is a novel but growing research topic which is attracting more attention with the growing availability of built-in sensors. This paper discusses the state of the art in this novel field of research and provides an overview of publicly available relevant databases and annotation tools. We finally discuss in detail challenges and opportunities in the field.