I've just come across an interesting source of 80,000 images available for non profit educational use.

The site WorldImages, is a database created by California State University. The categories of images include art & architecture; cities; social & cultural interactions; history, politics and warfare; music, drama & literature; natural world; people & portraits; religion, myth & magic; women; science, technology & mathematics.



There's also a page for course materials that includes images for Introduction to World Culture, Elementary School Art & Science, Art Studio, Art & Architecture Surveys.