In the movies someone usually pushes the propellor blade down. In this photo it appears the prop is being pulled up, and that a second person assists by ??pulling the first person out of harm's way?
I don't know. The photographer captured a curious moment in time.
(Found at Vintage Photographs)
Addendum: I realized while I was eating dinner (and "Leah" has already pointed out in the comments) that my use of "up" and "down" is dependent on which side of the plane the assistant is on (and frankly this guy could have started on the other side and come all the way across). I should have phrased it as starting the prop counterclockwise vs. clockwise.
None of this is very important; but it's still a curious photo.
Second addendum: Received a definitive answer from a relative who is a pilot and air traffic controller:
It is a WWI British (USA built them, too, and flew them long after the war with the air mail service) De Havilland DH-4. The prop spins clockwise (from the pilot view). They are pulling it up because they can't reach the tip of the upper blade to pull down on it. The second guy could be both pulling the other out of harm's way or adding extra power.