File:1966 NYC smog by Neal Boenzi NYT.jpg

Immediate source: https://www.nytimes.com/store/smog-covered-skyline-1966-nsap3661p.html

It will also be used in its capacity as the photograph used by The New York Times — an important paper nationally and within New York itself — to illustrate the 1966 smog.

Even if a free alternative image showing the historic smog were to emerge, it is unlikely to be of the same quality or from a similar vantage point. That is, another image from the same time period may technically show the smog, but it is unlikely to find another pictoral representation that depicts the smog over the city as its subject. Wiki users who may know of a free alternative in their grandparents' closet trove of photos are welcome to pitch alternatives, but an alternative photo would have to suitably depict the smog over the city, not merely a photo from the same time period in New York City that happens to include the sky.

Finally, even if a suitable replacement image is found for the top of the article to illustrate the event, the image would still be used lower on the page solely in its separate capacity as a historically and aesthetically significant image. From the NFC: "Two of the most common circumstances in which an item of non-free content can meet the contextual significance criterion are: ... where the item is itself the subject of sourced commentary in the article..." The article includes third-party commentary on the qualities and significance of the photograph itself.

The image has occasionally been used by sources other than The New York Times in high-quality resolution (see, e.g., its use here in Business Insider), but those uses are often misattributed (understandably and mistakenly) because a Flickr user uploaded it and falsely claimed it as his own work (see below for more).

AP Photo: I recently discovered an alternate, but still non-free, photograph of the smog by John Duricka for AP Photo. I thought I'd note the existence of this image, which does not have the same historical or aesthetic significance as the photo above, for purely informational purposes, for anyone out there who may be interested in other images. I think the AP photo's existence also incidentally bolsters the rationale for inclusion of this image, because the AP Photo shows that the image above is one of many non-free images that could have been selected, but is clearly the superior choice given its subsequent usage and commentary.