Lower Manhattan is a good place to take pictures for one boring, practical reason: the sights are close together. You can shoot a suspension bridge, a cobblestone street, a modern transit hall and the harbor in a single morning without getting on a train.
The catch is timing. Everything down here has two versions, the empty one and the crowded one, and the gap between them is about 90 minutes. The Financial District doesn't fill up until mid-morning, so the earlier you're out the door, the better everything on this list looks.
We've listed these with walk times from John Street, which is where we are, and the hour we'd actually go. All of them are free.
One honest note before you start: don't try to do all seven in one push. Pick three, walk them in order, get coffee. The list below runs roughly east to west, so it works as a route.