Rhetoric is in many of the images we see, even if we aren't aware of it. And sometimes, it's even just a matter of illustrating things that we might already recognize. As an example, in the Type and Image reading, they mention use of similes, among other rhetoric devices.
"His heart is as hard as a rock."
This is a sentence written in paper, but at the same time it's also something we can visualize. If anything, graphic rhetoric might have even more impact than written rhetoric, since seeing an image convey that message can be more immediate and emotional than just reading it on paper. I don't want to start an argument with some English buff, but it's just a thought.