Public Domain images are 'publicly available' and not covered by intellectual property or copyrights. There are many stock photography websites out there.
Free Images for Commercial Use - Free photos, stock photos, public domain stock photography.
Public Domain - Nature por takeabreak en Flickr
Japanese Designs (1902) | The Public Domain Review
Moon Face from an 1800s children's magazine. public domain graphic
Examples of Chinese Ornament (1867) | The Public Domain Review
Diagrams showing the trajectory of the major dives as performed at the 1912 Olympics in Stockholm x
All you wanted to know about public domain works - and why we can't expect new works until 2019 in the U.S.
Lovely illustration from Examples of Ornamental Metal Work, a public domain ebook downloadable in epub, kindle or pdf format here: https://archive.org/stream/examplesoforname00shaw
Illustrated initials from a German fairytale book (1919) | The Public Domain Review