Large Collections
The Ashmolean Museum
http://www.ashmolean.org/collections/
The Beazley Archive at Oxford University
http://www.beazley.ox.ac.uk/index.htm
The Bezalel Narkiss Index of Jewish Art at the Center for Jewish Art, Hebrew University of Jerusalem
http://cja.huji.ac.il/browser.php?mode=main
The British Museum Collection On Line
https://www.britishmuseum.org/research/collection_online/search.aspx
Louvre Museum
http://www.louvre.fr/en/moteur-de-recherche-oeuvres
Cabinet des Médailles
http://medaillesetantiques.bnf.fr/ws/catalogue/app/report/index.html
Staatliche Museen zu Berlin
Altes Museum
Antikensammlung
Bode Museum
Skulpturensammlung und Museum für Byzantinische Kunst
Münzkabinett
Neues Museum
Ägyptisches Museum und Papyrussammlung
Museum für Vor- und Frühgeschichte
Pergamonmuseum
Antikensammlung
The J. Paul Getty Museum
http://www.getty.edu/art/collection/
The Getty Research Institute
http://www.getty.edu/research/
The Israel Museum, Jerusalem
www.imj.org.il/imagine/collections/
The Metropolitan Museum, The Collection On Line
Late Antique and Early Christian Art, Third to Seventh Century
http://www.metmuseum.org/collection/the-collection-online
Museum of Fine Arts, Boston, Collections
http://www.mfa.org/collections
Perseus Digital Library
www.perseus.tufts.edu
Princeton Index of Christian Art
https://ica.princeton.edu/digital-image-collections/
TESS: sistema per la catalogazione informatizzata dei pavimenti antichi
http://tess.beniculturali.unipd.it/web/home/
The Walters Art Museum Digital Collection
http://art.thewalters.org/browse/
The Warburg Institute
Warburg Institute Iconographic Database
http://warburg.sas.ac.uk/vpc/VPC_search/main_page.php
Smaller collections
l'Album di Roma: Biblioteca digitale del Comune di Roma
http://www.albumdiroma.it/
Ancient World Image Bank, Institute for the Study of the Ancient World, NYU
http://isaw.nyu.edu/online-resources/ancient-world-image-bank
Ancient World Mapping Center, University of North Carolina at Chapel Hill
http://awmc.unc.edu/wordpress/free-maps/#sthash.1XTypFHV.dpuf
The British School of Rome Archive and Digital Collections
http://www.bsrdigitalcollections.it/
Cleveland Museum of Art, Medieval Art
http://www.clevelandart.org/art/departments/medieval-art
The Corning Museum of Glass (search under "Ancient")
http://www.cmog.org/collection/search
The Cult of Saints - Origins to circa AD 700, across the entire Christian world
http://cultofsaints.history.ox.ac.uk/
Eikon - Yale Divinity Digital Image and Text Library
http://divdl.library.yale.edu/dl/index.aspx?qc=Eikon
Emory University: Michael C. Carlos Museum
http://www.digitalgallery.emory.edu/luna/servlet/allCollections
Harvard Art Museums
http://www.harvardartmuseums.org/collections
The Jewish Museum, New York (has some antiquities)
http://thejewishmuseum.org/search/collection?keywords=Roman
Judaism and Rome. Re-thinking Judaism’s Encounter with the Roman Empire
Digital collections of literary records, epigraphy, numismatics, and material artifacts discussed in the ERC project "Re-thinking Judaism’s Encounter with the Roman Empire: Rome’s Political and Religious Challenge to Israel and its Impact on Judaism".
http://judaism-and-rome.cnrs.fr/
New York University, The Institute of Fine Arts
Early Christian and Medieval Art
http://guides.nyu.edu/c.php?g=276598&p=1844947
Princeton University Art Museum
http://artmuseum.princeton.edu/collections/1972/view
Real/Virtual: Representing Architectural Time and Space (Columbia University)
http://www.mcah.columbia.edu/ha/index.html
University of Haifa Digital Media Center Art & Archaeology Collections
http://digitool.haifa.ac.il/
Vanderbilt University, Jean and Alexander Heard Library
Art in the Christian Tradition
http://diglib.library.vanderbilt.edu/act-search.pl
VIA - Visual Information Access at Harvard University
http://via.lib.harvard.edu
Worcester Art Museum
http://vqs61.v3.pair.com:8080/emuseum/view/objects/asimages/1406?t:state:flow=f93fdde0-67fa-492d-a7a2-d68c72b829a4
Yale University Art Gallery
http://artgallery.yale.edu/collection/search