Search among openly licensed and public domain works.
Creative Commons Catalog API is a free Open Source Projects API that requires OAuth authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
Details from api.creativecommons.engineering.

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The Creative Commons Catalog API is provided by Openverse API (api.creativecommons.engineering).
Yes. The Creative Commons Catalog API is listed in the Open Source Projects 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 Creative Commons Catalog API uses OAuth authentication, so you need to register for credentials before making requests.
Yes. The Creative Commons Catalog API supports CORS, so front-end JavaScript can call it directly.
Yes. The Creative Commons Catalog API is served over HTTPS, so it's safe to use in production.