Determine a theme or central idea of a text and analyze in detail its development over the course of the text, including how it emerges and is shaped and refined by specific details; provide an objective summary of the text.
An image is a description that is meant to evoke emotion. So authors use imagery to create emotion. Imagery in writing serves to deepen the reader's understanding of what's going on and how to feel about it. The image is a tool.
I already know that someone answered this, but hey lol.