REMOVE

1. fences
2. railroads
3. barriers
4. hills
5. buildings (structures)
6. atmospheric perspective

WHAT

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

More 

WHERE

1. New York, New York (2)

WHO

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

WHEN

1. 1957 (1)
2. 1958 (1)