Register an Unsplash photo download (required by Unsplash when a photo is used).
Calls the Unsplash download-tracking endpoint for a photo and returns a temporary direct download URL. Calling this registers the download as an event for the photographer.
The Unsplash API guidelines require that, whenever a photo is actually used (downloaded, inserted into a document, set as a wallpaper or header, etc., not merely shown in a list of results), the app triggers this endpoint. This tool implements that requirement.
Call this once per actual use, ideally right before or as you use the image. It does not replace visible attribution: you must still credit the photographer and Unsplash with hotlinks (see unsplash_search). Use the returned url only for the download itself; for display, hotlink the urls.* fields from the photo object.
Unsplash photo ID being used.