Rawpixel is a good source for free images – photos, paintings, drawings, illustrations, etc. They also have a paid-for tier, with access to more images, but the free tier has lot of images.
Images are either free of copyright because the author of the image has made them so; or because copyright has run out and the images are in the public domain; or because they were always in the public domain.
An example of images that were in the public domain from inception are images commissioned by the US Government under the Farm Security Administration. Examples that come to mind are not on Rawpixel but rather in the US Library Of Congress collection.
This famous photograph by Dorothea Lange is an example. It is stored in the Library Of Congress, and is part of their digitised collection. All US citizens have rights to it.
It is entitled ‘Destitute pea pickers in California. Mother of seven children. Age thirty-two. Nipomo, California’ and otherwise entitled ‘Migrant Mother’
But looking at Rawpixel, if you look at their ‘Licences’ page you will see that ‘Free members can enjoy our free design resources for personal or commercial use’.
‘Free members’ means people who just go along to the site and download the images.
The following image from Rawpixel is a painting by Paul Gauguin.