How does Martin Luther King use imagery in "Letter from Birmingham City Jail"?

Imagery is a form of figurative language in which an author or speaker uses words and phrases to create mental pictures in the minds of the reader or audience. Mental pictures are created by using words related to the five senses: touch, taste, sight, sound, and smell. In his "Letter from Birmingham City Jail," Martin Luther King effectively uses imagery to capture the injustices his people are suffering.

In his letter, King is addressing a letter written by eight Birmingham clergyman, published in the Birmingham Post Herald. In their public letter, without directly using King's name, the clergymen protested against King's demonstrations being launched in Birmingham, and though the clergymen were against segregation, they were also in favor of patiently waiting for justice to be served. In his letter, King uses a sound image to protest against the idea of waiting for justice in order to promote active peaceful protest:

For years now I have heard the word "Wait!" It rings in the ear of every Negro with piercing familiarity. This "Wait" has almost always meant "Never." We must come to see, with one of our distinguished jurists, that "justice too long delayed is justice denied."

Here, in describing the word wait as a piercing, ringing sound, like an alarm bell, King is creating a sound image to relay how agonizing the word wait has become for African Americans. We know it is a sound image because we can literally hear the word wait being spoken by a person, and we can hear a piercing ringing sound, like an alarm bell. King uses this sound image to assert that now is the time for the African-American people to fight for justice.

Sight images are also found in the next paragraph that capture the extent of the injustices the African-American people suffer, such as in the following clauses: "vicious mobs lynch your mothers and fathers at will"; "when you have seen hate filled policemen curse, kick and even kill your black brothers and sister"; "twenty million Negro brothers smothering in an airtight cage of poverty." All of these are things we can actually see, so we know they count as sight images.