It appears that there is still a small park on Howard Street with the (probably) granite posts still there (Park Street is on the other side)- this is my best guess as to the site of the photo:

I think the dark lady was just caught in the frame, there seem to be several people just walking in the background. People used to walk around just to get air back in those days, or so I've heard. She appears curious as to what is going on. Possibly wondering why Mr. Nugent isn't nipping some covers.

The bollards are very reminiscent of the bilboquets in Magritte's canvases. And you can almost see that green apple floating in front of the boy's face. The woman reminds me a little of the female figure in Seurat's "Island of La Grande Jatte."

Nicely composed, lightly surreal photo. The boy seems so stiffly posed and ill-at-ease, with the blurry female striding up the path- one doesn't have to be a Freudian (I'm not) to wonder if earlier viewers might have found echoes of Herr Doktor there..

That hovering presence- it's Dainty Dora Standpipe!

"Unhand her Dan Backslide! You coward bully cad and thief!"

It looks to me as though this is a short exposure with a large aperture, seeing as how the boy is practically the only thing in the whole image that is in focus. You can see several other people deeper in the background, and none of them is motion-blurred.

It is a little curious why Hine would have composed it this way. Looking at the woman's skirt, it does seem that she might have been walking towards the camera; perhaps she was further away when he was setting up the shot and therefore didn't figure in his thoughts.

I agree with Seattlekid but it did give me a bit of a turn. I wonder if it would have been less creepy in color than in black and white.

When he developed the picture, Lewis Hine was amazed to see the woman in black in the background. "I'm sure there was no one there," he thought to himself. "Surely I'd have noticed." Puzzled, he went back, found the boy, and showed him the photograph to see if he could remember a woman. The boy turned white as a sheet. "That's....that's my mother," he stammered. "But...but...she died last year...."

Or maybe not.

It may be that the lady noticed that a photograph was being taken and paused so as to not interfere.

I don't know which Magritte painting you have in mind, but there's something surreal - eerie, even - about that woman just standing there in the background like some apparition.