Over the years a number of materials in the Graphic Arts Collection have been digitized. Some are connected to the online catalogue and some are not. Some are in the newer site DPUL and some in the older PUDL and some just online somewhere. Here is a list of the ones I can confirm, in case they are helpful to your research:
Antonio Martorell. Las Antillas Letradas https://dpul.princeton.edu/wa/catalog/nz8063470
Brother Jonathan Jubilee Pictorial newspapers http://pudl.princeton.edu/objects/9z903261b
Early Soviet Illustrated Sheet Music https://dpul.princeton.edu/catalog?f%5Breadonly_collections_ssim%5D%5B%5D=Early+Soviet+Illustrated+Sheet+Music&q=+Early+Soviet+Illustrated+Sheet+Music&search_field=all_fields
Franklin McMahon. Signing the Israeli/Egyptian Peace Accord, 17 September 1978 https://dpul.princeton.edu/wa/catalog/5138jj65g
Franz Freiherr von Wertheim’s Manuel de l’outillage des arts et métiers http://pudl.princeton.edu/objects/qr46r156v
Franz Hogenberg Engravings http://pudl.princeton.edu/collections/pudl0051
George Humphrey’s The Attorney-General’s Charges Against the Late Queen (50 caricatures) http://arks.princeton.edu/ark:/88435/dj52w599c
Gillett G. Griffin Japanese Woodblock Prints http://pudl.princeton.edu/collections/pudl0026
Giovanni Ottaviani after frescoes designed by Raphael. Loggie di Rafaele nel Vaticano https://dpul.princeton.edu/wa/catalog/5d86p388v
James Gillray Caricatures http://pudl.princeton.edu/collections/pudl0015
Jie zi yuan hua zhuan (Mustard Seed Garden Manual of Painting): http://arks.princeton.edu/ark:/88435/9z9031252
http://arks.princeton.edu/ark:/88435/kh04dr094
http://arks.princeton.edu/ark:/88435/fq977w17w
John Baptist Jackson Chiaroscuro Woodcuts http://pudl.princeton.edu/collections/pudl0031
Lorenzo Homar prints, drawings, and blocks http://pudl.princeton.edu/collections/pudl0033
Middle Eastern Film Posters http://pudl.princeton.edu/collections/pudl0100
Pathé Baby French silent movies https://library.princeton.edu/pathebaby/films
Photography album documenting the Morant Bay Rebellion in Jamaica (1865), the Indian Northwest Frontier Hazara Campaign (1867-1870), views of Malta, etc., 1860-1880 https://catalog.princeton.edu/catalog/5954033#view
Pencil of Nature by William Henry Fox Talbot https://catalog.princeton.edu/catalog/3696558#view
Princeton Print Club scrapbooks http://pudl.princeton.edu/objects/td96k526s
Richard Willats early photography album http://pudl.princeton.edu/objects/k930bx11x
Robert Nanteuil Engravings http://pudl.princeton.edu/collections/pudl0010
Sinclair Hamilton Collection of American Illustrated Books miniatures (1/4 done) https://dpul.princeton.edu/ga_treasures/catalog/v979v657w And other titles
Société Engelmann père et fils (3 vols. Chromolithography). http://pudl.princeton.edu/objects/3484zk471
Specimens of paper with different water marks, 1377-1840 http://pudl.princeton.edu/objects/k930bz393
Taller de Gráfica Popular http://pudl.princeton.edu/collections/pudl0012
Thomas Nast drawings and wood engravings http://pudl.princeton.edu/collections/pudl0039
Thomas Rowlandson prints and drawings http://pudl.princeton.edu/collections/pudl0130
Treasures of the Graphic Arts Collection https://dpul.princeton.edu/ga_treasures
Versailles on Paper, Books and Engravings
http://pudl.princeton.edu/collections/pudl0083
http://pudl.princeton.edu/collections/versailles2
http://pudl.princeton.edu/collections/versailles3