Imagery, despite the name, is not limited to visual descriptions. It is the use of language to engage the senses and create meaning that would be more difficult or inaccurately conveyed without its employment. For example, a description like "the ancient tree shivered in the breeze, its timbers creaking like a rusted hinge" is more evocative than saying "the tree was 2000 years old, and there was a breeze".
Imagery in The Help includes:
No, white womans like to keep they hands clean. They got a shiny little set a tools they use, sharp as witches fingernails, tidy and laid out neat, like the picks on a dentist tray. They gone take they time with them.
First, we might consider the dialect a form of imagery; it is difficult to "hear" the speaker unless one has previously heard this particular dialect spoken in real life, but if the reader has, then the speaker's tone and personality are given life through this characterization. The use of the words "shiny", "little", "tidy" all contribute to the depiction of order and daintiness. The "witches fingernails" lends a tone of unpleasantness, as though these tools are somehow threatening, unnatural or vicious.
“I throw back my coffee, watch a horsefly buzz against Aibileen’s screen door, knocking with its hard ugly head, whap, whap, whap, until it falls down on the step. Spins around like a crazy fool.”
In this case, the horsefly is really an allegory for stubbornness and the misfortune that stubbornness brings. This gives us an excuse to express the feelings that the character wishes to convey; we might feel a combination of pity and disgust at the fly, though we may not want to express these feelings about a stubborn human being. The quote employs an important imagery device; onomatopoeia, or sounds written as words. The "whap whap whap" is repetitive and unpleasant: we might think of a sound like "whap" as something that an inanimate object does, making the allegory all the more unflattering.
I always thought insanity would be a dark, bitter feeling, but it is drenching and delicious if you really roll around in it.
Here, the author employs the sense of taste (bitter and delicious) and touch (drenching and rolling) to describe an abstract concept (insanity). This is especially important because it's a fair assumption that most readers have never actually been insane, and would therefore have only a guess as to what it would feel like. This may be part of the reason for the author's choice of taste and touch to describe it; these are senses that we may not, at first, associate with insanity, which makes them all the more suited for it.