The imagery of John Donne varies throughout his writing life. In the beginning, Donne's imagery was meant as a metaphor for the satires which he wrote regarding common Elizabethan topics. These topics (politics, mediocrity in writing, and arrogant court people) were described with language that typically alluded to or blatantly depicted these topics with sickness and animal's manure.
After facing multiple personal conflicts (illness, financial problems, and deaths, Donne's poetry changed. The imagery took on a more calm and sedate feeling.
Renowned for his conceits (use of an extended metaphor which compares to completely different things into a singular idea), Donne was the master of imagery. One example of Donne's use of conceit appears in his poem "The Flea". Donne uses the biting and blood sucking of a flea to describe the union of a marriage.
That being said, Donne's imagery was the unchanging part of his poetry. While the message and satirised style of his early years is far from the more personal and religious works later, Donne's use of imagery always remained prominent.