Goal
The goal of any rhetorical analysis is to demonstrate your understanding of how the piece communicates its messages and meanings. One way of looking at this process is that you are breaking the piece down into parts. By understanding how the different parts work, you can offer insights as to the overall persuasive strategies of the piece. Often you are not looking to place a value judgment on the piece, and if there is an implicit or implied argument you may not be ultimately taking a side.
It’s worth asking then: is rhetorical analysis of visual documents any different than this basic description? Yes and no. Sometimes you will encounter an interplay of words and images, which may complicate the number of rhetorical devices in play. Additionally, traditional schooling has emphasized analysis of certain texts for a long time. Many of us are not so accustomed to giving visual documents the same kind of rigorous attention.