Flickr Services.
Flickr API is a free Photography API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
The safest and most inclusive global community of photography enthusiasts. The best place for inspiration, connection, and sharing!
Details from flickr.com.

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The Flickr API is provided by Flickr Services (flickr.com). The safest and most inclusive global community of photography enthusiasts. The best place for inspiration, connection, and sharing!
Yes. The Flickr 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 Flickr API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Flickr API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Flickr API is served over HTTPS, so it's safe to use in production.