Images can be used to define certain important areas in a poem. This can apply whether your poem is about nature, a person, a memory or any other subject. Many years ago the Chinese philosopher Wei T’ai said ‘poetry presents the ‘thing’ in order to convey the feeling. It should be precise about the ‘thing’ and reticent about the feeling, for as soon as the mind regrounds and connects with the ‘thing’ the feeling shows in the words, this is how poetry enters deeply within us.’ This ‘thing’ he refers to is an image.
This image may be in a line, a sentence or a phrase. Through imagery an emotion can be made evident, and it can also help to build up an atmosphere.
For example, the image at the start of the poem Fishing harbour towards evening by Richard Kell builds up atmosphere in the first four words: Slashed clouds leak gold. In the second stanza there’s another image in Abrasive squalls flake seagulls off the sky:/Choppy with wings the rapids of shrill sound. Lots of images here. Again, an atmosphere is defined in the poem Cold by Glyn Hughes: Tonight the brittle trees/rattled and snapped in wind and the stars broke/trembling like shattered ice.