9. A signal processing apparatus that is configured to generate annotation tags for classifying media and comprises memory and an associated processor that is configured to: receive media to be classified, said media received in electronic form; retrieve 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; represent 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; compare the features of the transformed media to explanatory representation data that, within the selected representation domain, represents bottom-level descriptors in the set of hierarchical descriptors of the annotation ontology tree; generate 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 apply one or more of the annotation tags to the media and thereby classify the media according to the applied tags.
9. A signal processing apparatus that is configured to generate annotation tags for classifying media and comprises memory and an associated processor that is configured to: receive media to be classified, said media received in electronic form; retrieve 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; represent 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; compare the features of the transformed media to explanatory representation data that, within the selected representation domain, represents bottom-level descriptors in the set of hierarchical descriptors of the annotation ontology tree; generate 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 apply one or more of the annotation tags to the media and thereby classify the media according to the applied tags. 11. The signal processing apparatus according to claim 9 , wherein the signal processing apparatus is configured to apply the one or more annotation tags in dependence on user input.