REMOVE

1. trees
2. sky
3. hats
4. rubbish
5. houses
6. oil paint

WHAT

1. Visual Works (hierarchy n … (1)
2. artists (visual artists) (1)
3. black-and-white film (1)
4. buildings (structures) (1)
5. bushes (1)

More 

WHERE

1. Westminster, Maryland (1)

WHEN

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