Image Optimization.
Image Upload API is a free Photography API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
Image Upload API is an image manipulation and optimization REST API.
Details from apilayer.com.

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The Image Upload API is provided by APILayer (apilayer.com). Image Upload API is an image manipulation and optimization REST API.
Yes. The Image Upload 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 Image Upload API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Image Upload API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Image Upload API is served over HTTPS, so it's safe to use in production.