A new service from Google, Google Art Project…
“Explore museums from around the world, discover and view hundreds of artworks at incredible zoom levels, and even create and share your own collection of masterpieces.”
Based on the Google Maps technology and its familiar interface, the images are gigapixel and presented without watermarks. Just 17 gigapixel images to start with, and there are also StreetView-like tours of their museums. If images look a little blurry as you zoom in, then simply give time for the tiles to load (in a similar way to Google Earth), and the sharper tiles should appear.
The “Add” button for the creation of personal collections doesn’t seem to work in Firefox.