The best way to make sure you are not violating Copyright is to use images and audio recordings you’ve created from scratch.
Public Domain works: Images, sounds, and videos that are in the Public Domain can legally be reused without attribution.
Creative Commons works: Increasingly, authors and producers and choosing to label their works with Creative Commons licenses. These licenses allow people to reuse an an author’s work under certain conditions. In general attribution is required.
Fair-use in Education: Copyright is designed to protect the authors (producers) of creative works from loss of revenue as the result of their work(s) being reused without compensation. If you are not detracting from someone’s earning potential and are re-using the works in a manner that can be considered to be creating a new product, you can probably reuse the works.