Tens of thousands of images from NYPL photograph collections have been digitized and made freely searchable online. In particular:
In the late 1930s/early 40s, and then again in the 1980s, the Department of Finance arranged to photograph every lot in each block of the five boroughs. These photos are now digitized and searchable online at the Municipal Archives. The 1940s collection was conducted by the Works Progress Administration - see the detailed guide to this collection. The 1980s photos are stills transferred to LaserDisc from 35mm footage. To find a building, the Municipal Archives advises to first determine the block and lot number, and then use the search term format “block=# AND lot=#.”