REMOVE

1. trees
2. plants
3. clouds
4. silhouettes
5. benches (furniture)
6. wells (structures)

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. barriers (1)
4. black-and-white film (1)

More 

WHERE

1. New York, New York (1)

WHO

1. Diane Still Knox; Diane K … (1)
2. Knox, Diane Still (1)

WHEN

1. 1958 (1)