Autorska prava/Copyrights

There are photo databases that you can download and use freely without citing a source. In this case, citing sources is a matter of personal choice and professionalism, not a legal obligation.

Some of these bases are:

Flickr
https://www.flickr.com/

Pixabay
https://pixabay.com

Reshot
https://www.reshot.com

Pexels
https://www.pexels.com

Foodiesfeed
https://www.foodiesfeed.com/

PublicDomainVectors
https://publicdomainvectors.org/

All additional information from open source sources 
can be found at the link:

https://wabisabilearning.com/blogs/technology-integration/15-open-source-image-resources