To be able to recognize imagery, one must first understand what imagery is. According to eNotes, imagery is
the forming of mental images, figures, or likenesses of things.
Imagery appeals to the senses of the reader: sight, sound, taste, touch, and smell. A good author can write about a scene, on object, or a place in such a way that the reader is able to create a full mental image of the thing described.
In Harper Lee's novel To Kill a Mockingbird, there are many places within the chapters (7-31) which contain imagery.
The following passage allows a reader to gain a sense of the seasons in Maycomb.
There are no clearly defined seasons in South Alabama; summer drifts into autumn, and autumn is sometimes never followed by winter, but turns to a days-old spring that melts into summer again. That fall was a long one, hardly cool enough for a light jacket.
Unfortunately, this description can really only be truly sensed by someone familiar with such seasons. Others may feel alienated by the subtle shifts from season to season. The imagery here is visual. Some engaged readers may actually be able to picture the actual change the seasons.
In this example, readers who are familiar with snow (which all are not) can see the snow and "mushy footprints." They can also "taste" a flake (brought on by remembering).
I looked back at my mushy footprints. Jem said if we waited until it snowed some more we could scrape it all up for a snowman. I stuck out my tongue and caught a fat flake. It burned.
Basically, any portion of text which allows a reader to sense and/or picture what Lee is providing as part of the descriptive passages is considered examples of imagery.