Some copyright holders allow people to use their creative works without specifically asking for permission, under specific circumstances. The best-known example is the Creative Commons license, which allows copyright holders to specify how their material can be used and if they allow for adaptations of their work. For example, this tutorial has a Creative Commons license, so other institutions can use and adapt it.
You can find works licensed in this way through a Creative Commons search. Just remember: Even though it’s free to use these works, you must follow the terms of the license and cite your sources!
