Over 550,000 images scanned from the holdings of the New York Public Library.

From their site:

Media: Artworks; fine prints; manuscript illuminations; maps; photographs; printed ephemera such as menus, post cards, posters, and trade cards; rare illustrated books; and other pictorial formats

Time periods: Middle ages to early- and mid-twentieth century predominate, although historical images of earlier eras may be found, as well as some post-1950 holdings

Subjects: The applied sciences, book arts, fine and decorative arts, history, performing arts, and social sciences; in other words, the established subject strengths of the vast collections of the Research Libraries

Geographical range: International with strong representation of New York, the United States, Europe, and the Far East

Organization: In most cases, this website presents holdings in their entirety; for example, when a group of materials is digitized, it means every print in a series, photograph in a folder, plate in a classic illustrated zoology, or trade card in a numbered run is represented by a digital image if it is owned by NYPL. Some holdings are presented as they are organized and kept by library divisions and curatorial departments, and as they might be accessed in the Research Libraries' study rooms. Other materials, primarily books and portfolios, are presented in groupings by artist or topical theme in order to bring together works that relate to a common creator or subjects, but were acquired from various sources or are held in different physical locations.