Unsplash's API lives at https://api.unsplash.com. Its guidelines require hotlinking the returned image URLs and crediting the photographer.
Register an app at unsplash.com/oauth/applications and send its access key as Authorization: Client-ID <key>. In the examples it's written {{UNSPLASH_ACCESS_KEY}}.
Full reference: https://unsplash.com/documentation
curl "https://api.unsplash.com/search/photos?query=taco&per_page=2" \
-H "Authorization: Client-ID {{UNSPLASH_ACCESS_KEY}}"curl "https://api.unsplash.com/photos/random?query=mountains" \
-H "Authorization: Client-ID {{UNSPLASH_ACCESS_KEY}}"