Like any rhetorical analysis essay, an essay analyzing a visual document should quickly set the stage for what you’re doing. Try to cover the following concerns in the initial paragraphs:

Make sure to let the reader know you’re performing a rhetorical analysis. Otherwise, they may expect you to take positions or make an evaluative argument that may not be coming.
Clearly state what the document under consideration is and possibly give some pertinent background information about its history or development. The intro can be a good place for a quick, narrative summary of the document. The key word here is “quick, for you may be dealing with something large (for example, an entire episode of a cartoon like the Simpsons). Save more in-depth descriptions for your body paragraph analysis.
If you’re dealing with a smaller document (like a photograph or an advertisement), and copyright allows, the introduction or first page is a good place to integrate it into your page.
Give a basic run down of the rhetorical situation surrounding the document: the author, the audience, the purpose, the context, etc.

Source: https://owl.english.purdue.edu/owl/resource/725/03/

ELTA 101 ROAD MAP: SOAPSTones Rhetorical Analysis Essay Structure