Clip art, photos and images free for Educational (non commercial) use [though not necessarily copyright free]

National Education Network (NEN) Gallery

2Simple clipart linked to topics in the curriculum

Dorling & Kindersley Range of high quality digital photos covering a number of curriculum topics

East Riding RBC images from the East Riding Regional Broadband Consortium

Northumberland Grid Clipart linked to topics in the curriculum

EB2N (Midlands RBC) photograph library

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.

US Clip Art US Images linked to US school topics

A picture search engine which shows the range of pictures to match your search.
Links to the source. (n.b. Users would need to check the copyright against each sourced picture).