"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" (Free, copyright-friendly images for education, ¶1, 2012.11/01).
Access point for help and tutorials - Categories include: Getting Started; Organizing your Docs List; Creating and Editing Drawings; Sharing, Collaborating and Publishing; Uploading and Exporting; Fixing a Problem; and More.
In this blog post (2014.09.30), Sabio Lantz (pen name) represented the history of the English Language in a single diagram. The main source of info. for that diagram was another website to which there is a link at the end of the post.