Photography.
Unsplash API is a free Photography API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
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Details from unsplash.com.

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Stock Photos and Videos
The Unsplash API is provided by Unsplash (unsplash.com). Create with the largest collection of high-quality images that are free to use. Trusted by Trello, Medium, and thousands of other API applications to power their free picture needs.
Yes. The Unsplash 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 Unsplash API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the Unsplash API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Unsplash API is served over HTTPS, so it's safe to use in production.