Consider a picture of a unicorn. Let's say the occlusion shape of an object is its outline or silhouette from a particular perspective. Consider the following principle.

http://coloringpagesfun.com/my-little-pony-unicorn-coloring-pages/

If a picture represents an object, then the occlusion shape of an object must be identical to the smallest part of a picture that depicts it.

Since there are no unicorns, then a picture cannot represent one. John Hyman revises this principle distinguishing between an "external subject" and a "internal subject." Roughly,

If a picture represents an internal subject, then the occlusion shape of the picture's internal subject must be identical to the smallest part of a picture that depicts it.

This avoids the above problem since the internal subject (the unicorn) can have the same occlusion shape as the smallest part of the picture that depicts it.

Question: Do you find this necessary condition of Hyman's account of pictorial representation plausible? Are there any implausible consequences of his view?