What does the term still life mean?

A painting or drawing of an arrangement of object, typically including fruits and flowers and objects contrasting with these in texture

Diamond or a rectangle or a triangle

Artists usually use musical imagery to make their compositions more unique and alive. imagery in music used to "show" music. because of that listeners feel what happens. they see music like complete composition. they hear sounds, they feel movement, they see a picture. it makes music deep. that's why  musical imagery is very important and is used by artists so frequently.