To represent actions, ideas and objects in a way that it appeals to the senses through the use of figurative language are referred to as imagery.
Imagery is used to create sensory details, that is, it is used to make the readers think more deeply by uses the senses (smell, visual, feeling, touch and sound)
Through imagery, it helps the reader in drawing specific details about the text which leads to the interaction between the text and the reader.
Whereas, repetition refers to the something which is being already said and written is repeated. In other words, it refers to the recurrence of events and actions.
Hence, both imagery and repetition are used to create the effect of language and is often word-choice extension.