That’s a picture of the second Brooks Brothers store taken, according to the pencil notation at the bottom, around 1865. The store was on the northeast corner of Grand Street and Broadway, at 462 Broadway; the cast-iron-front building there now was constructed in 1880. Without a fairly deep dive into archives it’s difficult to say when the old building was constructed, but its style, and particularly the heavy masonry wall over first-floor partially-cast-iron storefronts, is similar to a lot of 1830s and 1840s commercial buildings in lower Manhattan.
The photo has everybody’s favorite artifact of mid-1800s pictures: the long exposure time necessary back then makes everything that moves into a ghost. The woman standing near the curb directly above the word “corner”, the horse and carriage on the right, the flag on the roof, and the omnibus on the lower left were, as far as I know, not actually ghosts. They just moved during the exposure while the building did not. It’s a slightly creepy effect but beautiful. The man in a white shirt and vest peering out a second-floor window must have stood still, as he looks solid; the man two windows to his right with a leg out the window was moving.
The mystery, and the reason I found this photo interesting, is the skeletal awning running from both street facades to the curb. The cast-iron poles at the curb look permanent and don’t serve any obvious function other than holding the awning roof. The awning roof frame is wood with some effort at proper construction: the top ends of the rafters have birds-mouth cuts to fit the second-floor water table; the lower ends appear to have some kind of metal strap connection to the metal bar running pole to pole. There’s another metal bar on top to the top connections, which could be some kind of hold-down.
Full-sidewalk awnings are not and never were common in New York, and those that were built in the 1800s were typically more permanent than this. This might have been there for the summer, to keep the sun off window-shoppers and perhaps have passers-by associate Brooks Brother with a few moments of relief. In that scenario, the canvas would be removed in the winter to prevent snow build-up. I certainly want to think that the fellow with one foot out the windows is part of a maintenance team either putting the canvas out or taking it in. It also could be there to prevent snow from reaching the sidewalk, but that was not a practice here at that time (unlike using awnings as sunscreens, which was) and the framing looks too light to have successfully carried snow.
The lower bar is sagging midspan between the poles, telling us what we already knew: none of this structure was designed in an engineering sense. The wood is straight, but wood creep requires reasonably constant load and if the canvas was only present for four months per year, that might take a long time. Also, I wouldn’t be at all surprised if the awning roof blew down in a storm once in a while and had to be wholly or partially rebuilt.
Without a properly-dated picture of the building with canopy up or a description, it will remain a mystery.