Public Domain Pictures
Tons of images in the public domain that are searchable. You can pay for premium downloads.
“MyOpenMath runs on the open source, IMathAS platform, providing free hosted use of this platform in support of free, open textbooks like the ones listed on OpenTextBookStore.com. The intent is to provide classroom use of the platform, without any required cost to students, for schools wanting a managed install of the IMathAS platform, and to provide students self-study opportunities.”