Online Image Collections

Finding images of ancient art online can be a confusing and frustrating process. Google image searches don't really scratch the surface. That said, museums are the best place to go for images of ancient art. However, not all museums offer online collections, and the various rights reserved for those images is a rat's nest. Generally speaking, Wikimedia and Flikr photographers are the best online source for publicly available images of artefacts kept in museums that do not offer online collections, which is most of the museums in Germany, Italy, and Greece.

What follows is an alphabetical list I've compiled of online resources for the study of Classical art and a brief description of their respective usage (copyright) policies.

Ashmolean, Oxford Collections is slow to connect from the US. Copyright of images is on a per artefact basis, but those held by the University are free for educational, non-commercial use. Click here for their full terms of use page.
Boston Museum of Fine Arts has one of the best collections of Archaic and Classical Greek art, some really iconic pieces. Unfortunately, the files available for download are rather limited, but they do offer multiple angles of many works. Recently, it appears they have cut back on the quality (color vs. black and white) of images they show on the site. I'm not sure if that is a long-term situation.
British Museum Collections is one of the largest and easiest to use collections online. All of their images are copyrighted with few restrictions (CC BY-NC-SA 4.0) as long as they aren't used commercially.
Chazen Museum of Art is an excellent online collection of easy to access information and quality images for study online. Images are copyright protected and are not readily available for download.
Cleveland Museum of Art offers a small but very useful collection of Classical images using the CC0 1.0 designation (completely free use, public domain).
Egisto Sani (Flickr) is an Italian professional photographer who publishes photos of artefacts in museums throughout Germany, Italy, Greece, and others. The photos are of very high quality and tend to focus on the painting rather than the vessel itself when dealing with vases. Although some photos are all rights reserved, the vast majority are free for non-commercial use with attribution (CC BY-SA 2.0).
Gary Todd (Flickr) is a professor of history at the Sias International University, China. He is an amateur photographer and posts a slew of artefacts from museums and historic sites throughout Europe, Asia, and beyond. Individual artefacts are not cataloged and described in the painstaking way that Egisto Sani organizes his work. However, Professor Todd's photo albums are organized by location, and they contain many artefacts held in Greek and Italian museums that do not publish online collections. The down side is you might need to know what you're looking at based on your own expertise. Note that while all of his photos are listed as Public Domain, many of the museums almost certainly restrict photography to non-commercial use.
Getty Museum Collection is my favorite. This museum publishes all of its images as Public Domain Dedications (CC0 1.0).
Harvard Art Museums offers a relatively small collection of Classical images "for personal, noncommercial use, including educational and scholarly purposes." They also offer higher resolution images for free, but those images are not liscenced for reproduction without separate written agreement.
Louvre Collections is one of the most extensive online repositories in the world (as one would expect from the most famous museum in the world!). All of the images are copyrighted, and there are various copyrights depending on the photographer, but as a general rule, the images are freely available for personal, educational, noncommercial use. Although the site is available in English, the artefact descriptions are only available in French.
Metropolitan Museum of Art (MET) is another favorite of mine. Like the Getty website, all artefact images in the MET collection have been released to the Public Domain via the museum's Open Access policy. The collection is larger than the Getty's, but it doesn't rival the British or Louvre collections.
Museum Fur Kunst Und Gewerbe, Hamburg (MKG) is a fantastic collection of public domain artifacts. The English language site does not translate artifact information into English, but a decent web browser (e.g., Firefox) or plugin will do a serviceable job. Hint: if you select the German site (DE), most browsers will pop-up a button to translate the page for you without going through a menu.
Rhode Island School of Design (RISD) Museum offers a modest collection of Classical art images that, like the Getty and MET, are made freely available on the Public Domain (CC0 1.0)
Toledo Museum of Art offers an easy to search collection of Classical art. The images and descriptions are very helpful. Images themselves are copyrighted and not readily available for download.
Virginia Museum of Fine Arts (VMFA) has a good colleciton of well-presented art, most of which is available for download under Creative Commons CC-BY-NC, which is public permission for anyone to reuse the media for noncomercial activities.
Walters Art Museum hosts a medium sized collection of Classical art that is, once again, released to the Public Domain (CC0 1.0) with no conditions.
Wikimedia Commons is the visual arm of Wikipedia, and houses a slew of images from museums and Classical sites around the world taken mostly by amateur photographers. Rights usages vary by the author, but for the most part, the usage rights are free to share or modify with attribution (e.g., CC By-SA 4.0). Many are released entirely to the Public Domain. Others are limited to noncommercial use by the museums in which the photos were taken.
Yale University Art Gallery Collections offers some 11,000 artefacts (or fragments) from the Greek world, all via the Open Access policy adopted by the MET (CC0 1.0).