REMOVE

1. sky
2. silhouettes
3. branches (plant components)
4. clouds
5. farms
6. buildings (structures)

WHAT

1. Visual Works (hierarchy n … (1)
2. benches (furniture) (1)
3. black-and-white film (1)

More 

WHERE

1. Westminster, Maryland (1)

WHO

1. Campbell, Sandra L. Still (1)
2. Sandra L. Still Campbell; … (1)

WHEN

1. 1961 (1)
2. after 1961 (1)