We have recently digitized some of our police related special collections, try searching Police and New York in our Digital Collections.
Woodcut illustrating the first NYPD uniforms in 1854.Detail from this image digitized from the Riccio Collection
Portrait of Edward O. Shibels, Police Officer, 19th Precinct, Image digitized from the Shibels Family Papers.
Search YouTube for NYPD Videos
Video and Sound Collections databases available from John Jay Library
The Library of Congress Prints and Photographs division has digitized images from the NY World Telegraph & Sun Newspaper which includes many photos of police, including mugshots.Their American Memory Project also has image and other resources on police, including a film of a Police Parade from 1899.
The NYC Municipal Archives has digitized some images of Crime and Criminals, which include NYPD mug-shots. There are also over thousands of images found in the search "New York AND Police" in their online gallery. Also At the Municipal Archives of NYC -NYPD Surveillance Films 1960s-1980s.
The Brooklyn Public Library has digitized the photographs collected by the Brooklyn Daily Eagle, which are searchable together with their other historic photographs here.
The New York Public Library Digital Collections has many images related to the NYPD and Police
Police Work: Leonard Freed’s photographs of the NYPD Revisiting the daily life of New York City's Police Department during the famously tumultuous 1970s from Magnum Photos