Imagery refers to descriptions that appeal to the five senses. The strongest imagery in Dickinson's poem is visual and tactile, appealing to the senses of sight and touch. Beyond that, Dickinson's use of sound devices suggests auditory imagery as well.
The visual images Dickinson creates are of the carriage in which the personified concepts of Death and Immortality ride--conjuring an image of a gentleman caller and a chaperone. Visual images of a school with children fighting in a playground and a sunset shining upon fields of grain follow. The "swelling of the Ground" that is the grave is easy to picture, and the "Horses' Heads" wording allows readers to visualize the horse-drawn carriage at the end.
The tactile imagery evokes the feeling of movement when Dickinson says "We slowly drove" and repeats "passed" several times. In stanza 4, the feelings of temperature and texture are quite strong with the descriptions "The Dews drew quivering and Chill," and "only Gossamer, my Gown -- My Tippet -- only Tulle." Readers can almost feel the cool air on their skin under the filmy garments.
Although there are no overt sound descriptions, Dickinson's choice of words creates some sound imagery as she uses alliteration and consonance to stand in for the sounds she doesn't describe. In the beginning of the poem, the hard /k/ sounds of because, could, kindly, and carriage bring to mind the clopping sound of horses' hooves. The word quivering is mostly tactile, but it has a slight auditory aspect to it as one thinks of teeth chattering or a rustle caused by something that quivers. In the final stanza, in the cemetery, the hushed /s/, /sh/, and /h/ sounds in the words since, Centuries, shorter, surmised, Horses', and Heads create the feeling of being in a silent and still graveyard.
Dickinson's haunting poem contains rich visual and tactile imagery, and through skillfully applied sound devices, it creates auditory sensations as well.