How to check if you can legally use materials in your teaching
To check if you can legally use materials, you can check if the creator of the work has attached a licence to the work that will allow you to use it under certain conditions, for example:
You can check if the copyright in the work has expired. If it has, the work will be in the public domain and free to use.
See the Australian Copyright Council’s information sheet on Duration of Copyright to find out when copyright in a particular work expires.