ReSmush.it vs Unsplash

ReSmush.it is a free, keyless image-optimization API — best known as the backend behind the ReSmush.it WordPress plugin — that accepts a source image URL and returns a JSON payload with the compressed image's URL plus original size, compressed size, and percent reduction. A live call against api.resmush.it needed no credentials and returned Access-Control-Allow-Origin: *, so it works directly from browser JavaScript. The plain http:// endpoint immediately redirects to https, so the service is https-only despite requiring no API key.

Unsplash's JSON API lets apps search, browse, and download from its library of freely licensed photos, returning dynamically resizable image URLs (powered by Imgix) alongside photographer and collection metadata. Nearly all real use is covered by a static Client-ID access key sent via the Authorization header — full OAuth is only needed for a handful of actions performed on a user's behalf, like liking a photo. New applications start in demo mode at 50 requests/hour and can apply for production approval to reach 1,000/hour, with attribution to the photographer and Unsplash required under the Unsplash API Guidelines.