1. A method of generating annotation tags for classifying media, said method performed by a signal processing apparatus comprising a processor and a memory, and said method comprising: receiving media to be classified, said media received in electronic form; retrieving an annotation ontology tree associated with a respective media class and comprising a set of hierarchical descriptors for labeling objects or things with increasing specificity; representing the media within a selected representation domain by applying a corresponding signal transform to the media to obtain a transformed media comprising features characteristic of the media in the selected representation domain, wherein the selected representation domain is non-human perceivable; comparing the features of the transformed media to explanatory representation data that, within the selected representation domain, represents bottom-level descriptors in the hierarchical set of descriptors of the annotation ontology tree; generating a set of annotation tags from one or more of the hierarchical descriptors in the annotation ontology tree that correspond to any of the explanatory representation data that, based on the comparing, are identified as matching the features of the transformed media; and applying one or more of the annotation tags to the media and thereby classifying the media according to the applied tags.