I recently wrote about the construction of buildings like Rockefeller Center in New York during that period here. The OP asked a similar question about the photograph “Lunch Atop a Skyscraper" that I didn't address at the time.

The image to which you refer was created as part of a promotional campaign for the RCA building, which was part of the new Rockefeller Center complex. Archival records show it was taken on September 20, 1932 and first published in the New York Herald Tribune on October 2.[1] The identity of the photographer has never been confirmed. Charles C. Ebbets, Thomas Kelley and William Leftwich have been proposed, as they all worked for the news agency invited to the press event that day, but the photo was not credited to an individual at the time.

The famous photo shows 11 men lunching on a girder on the 69th floor while the building was still under construction. Over time, various assertions as to the identity of the workers have been made, including Irish immigrants and members of the Mohawk nation.[2] This is consistent with our understanding of the makeup of the workforce at New York City building sites in the period.

As I explained in my other response, skyscraper laborers at this time were not provided with or required to use safety equipment like harnesses. Workers were expected, for example, to walk across narrow beams untethered and show courage in the face of dangers like dizzying heights, loud noise and heavy machinery.[3] The relaxed and casual attitudes on display in this photo are familiar from other images of the period, such as the 1930 film made during the construction of the Manhattan Company Building that I discussed in the other thread.

But while the photo is not fake, it also not a candid snapshot. The photographers present that day were obviously not part of the construction crew in their semi-formal business attire complete with necktie, suspenders and stylish spectator shoes. The image was shot on a fragile gelatin dry plate negative using a bulky large-format camera with bellows that required careful reloading after each shot, of which there were many—including workers appearing to nap on the very same beam. The laborers would have been well aware of the photographers’ presence and likely required by their bosses at Rockefeller Center to respond to their instructions in order to create a compelling image for reproduction in the press.

This photograph has since become one of the most recognizable and reproduced images in the world. The original negative, now partial and cracked, currently resides in a climate-controlled storage facility in Pennsylvania.

Sources:

[1] Ben Goldberger, ed. 100 photographs: the most influential images of all time. New York: Time Books, 2015.

[2] John Anderson. "How a Galway Pub Led to a Skyscraper," New York Times. 11 Nov. 2012: AR.16.

[3] Jim Rasenberger. High Steel: the Daring Men Who Built the World's Greatest Skyline. New York: HarperCollins, 2004.