REMOVE

1. hats
2. rubbish
3. trees
4. automobiles
5. hills
6. boys
7. buildings (structures)
8. barriers

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. berets (1)
4. 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. 1965 (1)
3. between 1961 - 1965 (1)