Choosing a nature image
Pick the shape first: a wide landscape for a hero or a slide, a tall one for a poster or a phone screen. Leave room for text: skies, water and out-of-focus backgrounds take a headline well, busy foliage does not. For print, check the pixel size: a full A4 page at 300 dpi needs about 2480 × 3508 pixels.
Where free nature images come from
Wikimedia Commons holds millions of nature photos with a licence recorded per file. Openverse indexes Creative Commons photos from Flickr and other sites. Museums such as the Met and the Cleveland Museum of Art publish public-domain natural-history prints and paintings. Unsplash, Pexels and Pixabay have large modern libraries; they can't be searched automatically here, so each search links straight to the same query there.
Licences for nature images
Landscapes rarely need releases, which makes nature one of the safest kinds of image to use commercially. Check the licence itself: CC0 and public-domain images need nothing, CC BY needs a credit line, and CC BY-SA means an edited version must carry the same licence. Recognisable people or private buildings can still need releases for ads.
