When an author creates imagery, he or she uses words that create a mental picture in the reader's mind. Only sensory words can create mental images; therefore, imagery concerns any words or phrases that pertain to the five senses: touch, taste, sight, sound, and smell. In contrast, abstract concepts such as love and sorrow do not create mental images; however, an author can surround such abstract concepts with imagery in order create a picture in a reader's mind that helps the reader better understand the point being expressed concerning the abstract concept (Literary Devices, "Imagery"). Maya Angelou's poem "Caged Bird" is certainly full of imagery in every line and every stanza.
The very first image we see is that of a "free bird" leaping on the "back of the wind." Since we can literally see a bird in nature leaping, jumping, or flying against the wind, we can see how this counts as a sight image. Other images we see are that of the bird floating "downstream" and dipping its wing "in the orange sun rays." Since the poet is now speaking of a bird in relation to a stream, we get the sense she is speaking of a waterfowl, like a duck. Plus, since we can literally see things floating downstream we know that the phrase "floats downstream" counts as a sight image. In addition, though a bird will not literally dip its wings into the rays of the sun, we know that the sun's rays reflect on surfaces of water. Hence, based on the final couple of lines in the first stanza, we can picture the bird literally dipping its wings into the image of the sun reflected on the water and then flying off into the sky. Since we can literally see a bird doing such things in nature, we know that these count as sight images as well.
The sight images of the bird free in nature stand in great contrast to the sight images of a bird held captive in a cage in the next stanza. The juxtaposition of images of free and caged birds help to illustrate her themes concerning the effects of captivity, such as slavery.