
Wallpapers.
Wallhaven API is a free Photography API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
wallhaven.cc help docs!
Details from wallhaven.cc.

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Stock Photos and Videos
The Wallhaven API is provided by wallhaven.cc (wallhaven.cc). wallhaven.cc help docs!
Yes. The Wallhaven API is listed in the Photography category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Wallhaven API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Wallhaven API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Wallhaven API is served over HTTPS, so it's safe to use in production.