All of these sites have licenses granting you all rights on the pictures with and without naming the photographer. Even the right to modify and redistribute the pictures. Unless using the pictures to create a similar service.
www.pixabay.com
www.pexels.com
https://unsplash.com
and when it comes to icons then you will find here great variety of sources
18-best-websites-to-download-free-icons-for-commercial-use
