Pgannon I think you are right in your comments, but if I read them correctly you are probably leaving out the issue of the images being "received directly by the brain" and not going through the five senses. As I would understand it myself, you're right that all things give off "films" of atoms and that this explains vision, but it is also clear that they discussed receiving images while asleep - a time in which the eyes are closed and not the mechanism.
Lucretius is pretty clear that this is an important aspect in his discussion in Book 4. It even appears in the correspondence of Cicero and Cassius in their joking back and forth about "spectres."
I also recommend Dewitt discussion of images of you have not yet read his book.
Yes it is a fascinating subject!