Here are some links to clipart for educational us. Thet are not entirely copyright free.
Clip art, photos and images free for Educational (non commercial) use [though not necessarily copyright free]
National Education Network (NEN) Gallery
East Riding RBC images from the East Riding Regional Broadband Consortium
Photographs covering a range of topics
Pictures for free - copyright "friendly" - so double check!
Arkive: images and movie clips of wildlife - UK and global [need LGfL log-in as an LGfL asset]
WikiPaedia Commons - open-content material to which anyone can contribute. It supplies much of the material used to illustrate the community-written encyclopedia Wikipedia. All files uploaded to the Wikimedia Commons are available royalty-free for any purpose. The creator or photographer normally must be given credit, and some files are governed by "copyleft" licenses, meaning that works derived from them must be made available on the same terms.