This article presents an overview of ontology based digital image representation. An ontology is a specification of a conceptualization to create a vocabulary for exchanging information, where conceptualization mean a mapping between symbols used in the computer (i.e., the vocabulary) and objects and relations in the real world. In this paper, digital image semantic annotation by ontology and a novel ontological approach that formalizes concepts and relations with respect to image representations for data mining – the Image Representations Ontology (IROn) – are examined.