Google has a implemented a new tool for image searching: Sort by subject. It is sort of a visual help, as it suggests some categories for the subjects you are looking for. For instance, for « Pluto », I’ve got « Pluto planet », « Pluto dog », « Pluto god ». In italian, it was different, as it was: « Plutone pianeta », « Plutone e Caronte », « Plutone simbolo », « Plutone divinità », « Plutone e Proserpina », « Plutone Ade ».
In fact it is already available in different languages, among which English, French, Spanish and Italian, and the results are dissimilar.
Patrick Peccatte talks about it in its blog, pointing out some good and some bad features.