The Department of Information Technology and Telecommunications, GIS Unit, is providing the raw orthoimagery for download. This orthoimagery is used to create the Aerial Photography Tile Layer services described in further detail here: https://maps.nyc.gov/tiles/. Full metadata on the Aerial & Orthoimagery can be found at: https://github.com/CityOfNewYork/nyc-geo-metadata/blob/master/Metadata/Metadata_AerialImagery.md
The 2010 Orthoimagery Tile Index can be used to geo-reference the individual image tiles across the City (https://data.cityofnewyork.us/City-Government/2010-Orthos-Tile-Index/chzg-3b9u)