When we think of imagery, we are talking about images that the author or poet creates using words that appeal to our senses to help us imagine them. Therefore, generally speaking, the most successful images are those that appeal to as many of our senses as possible. When we think of this poem, and the complete picture that the speaker builds up of his mistress and of her many imperfections, we can see that the imagery he employs does appeal to many of our senses. Consider, for example, the dominant sense of sight:

My mistress' eyes are nothing like the sun;
Coral is far more red than her lips' red;
If snow be white, why then her breasts are dun;
If hairs be wires, black wires grow on her head.

We have a very strong visual description of the eyes being "nothing like the sun," her lips not being like "coral" and her "breasts" being a "dun" colour. In addition, the last line points towards the feel of the mistress' hair, stressing the sense of touch as we can imagine the rather unpleasant feeling of the speaker as he goes to touch his mistress' hair.

There is a definite appeal to scent in the fragrance that the mistress exudes, as the "breath that from my mistress reeks" captures, and an auditory image is captured in the sound of her speech, even though "music hath a far more pleasing sound." Thus we can see that this poem successfully appeals to a number of the senses to create excellent imagery.