These research guides give more information about using ARTstor and images in general.
While most major museums have websites, not all have substantial digital collections. Here is a selection of museums in the United States, Europe and Asia that do.
A database for international architecture, archINFORM includes images of and information about over 44,000 projects, most from the 20th century. Some entries, such as the one for the Farnsworth House (Mies van der Rohe), include multiple images, plans, and a bibliography.