REMOVE

1. horizon line
2. sky
3. flags
4. snow (precipitation)

WHAT

1. Visual Works (hierarchy n … (1)
2. black-and-white film (1)
3. boys (1)
4. coats (garments) (1)
5. fields (land) (1)

More 

WHERE

1. Bow Island, Alberta, Cana … (1)

WHEN

1. 1912 (1)
2. 1920 (1)
3. between 1912 - 1920 (1)