Pics4Learning is a safe, free image library for education. Teachers and students can use the copyright-friendly photos and images for classrooms, multimedia projects, web sites, videos, portfolios, or any other project in an educational setting.
Great photos for use for educational presentations, inc iPad pics and close ups of dictionary definitions for educational words, e.g. Teach, learning etc etc.
Search for CC pictures with Wylio, which allows you to choose the size of the image you want, and gives you the attribution all wrapped up in an embed code - very nice.