Free pictures:
Pexel https://www.pexels.com/ - all the photos on Pexels are licensed under the Creative Commons Zero (CC0) license. 
Creative Commons search: https://search.creativecommons.org/
Free digital photos http://www.freedigitalphotos.net/
Pixabay https://pixabay.com/
More: 21 sites with free stock photos: https://blog.snappa.com/free-stock-photos/

Free music:
http://incompetech.com/
https://biteable.com/blog/tips/how-to-find-royalty-free-music-video/

How to Search and Attribute Open Source Images the Right Way by Lee Watanabe-Crockett

https://globaldigitalcitizen.org/search-attribute-open-source-images