ABSTRACT
In the natural world, the propensity of animals to confuse the visual appearances of different entities is widely exploited in the form of camouflage and mimicry. The appearance of the distinctive Mexican hat has not only been used in relation to astronomical phenomenon. The difficulty of images representing a species is mirrored in disease classification systems; if too general it is useless, too detailed it becomes unmanageable. In nosology the concept of a spectrum of manifestations or severity is a useful means of describing a wide variation of phenotypes and genotypes. Radiological signs are also a product of human imagination, if not quite so world-changing. Western art has always relied on a set of readily identifiable figures and motifs, drawing upon religion and mythology.
