The Washington Monument is listing leftward in this picture, as are the trees in the park. That's an artifact of 1914 photographic technology, which utilized a slit in a spring-wound sheet-metal shutter to allow light focused by the lens to reach the glass-plate film. The slit would drop from top to bottom to expose the plate, but because there was a lens in front of the slit that inverted the light rays, the plate was actually exposed from bottom to top. And meanwhile, for this picture, the photographer was panning from left to right to follow the moving horse. Objects that weren't moving kinda got an angle to them.
A couple of years ago, the Washington Monument came close to acquiring a much more serious lean. The monument took a $15-million blow from a 5.8 earthquake and remains shrouded today in scaffolding, for repairs that probably are not considered important during a government shutdown, even though half the bill has been covered by a private philanthropist. We just can't have nice things any more because, you know, because.