I'm building a shortcode that display's a list of items from a public API, that each have a thumbnail URL. If I use the URL as src attribute, I create a request to their server for every image.
I want to prevent hot linking their images by caching them. I imagine the function to create the img-tag could cache every image it displays. Then, when it's to be displayed again, the URL is recognized, and I can link the cached image instead.
Is there a WordPress solution available for caching images so that they don't appear in the media library? I could use the file system and save them in a separate uploads folder, but if there is a standardized way, I would prefer that.
The list itself is already cached using transients.