Cache-control headers on responses from image server

[lizadaly]

Hello, and apologies if this isn't the right place to ask this—I'm happy to redirect my question elsewhere.

I'm working on a client that will make use of IIIF manifests that point at https://colenda.library.upenn.edu/ and I've noticed that images returned from Image API requests to this service (e.g.) have no Cache-Control header in the response. I believe this is causing browsers to never cache these images, even when they're unchanged.

Is this behavior intentional? I would think that it might be preferable to have nginx directives to indicate that these resources don't change frequently and are cachable, e.g.:

expires 30d;
add_header Cache-Control "public, no-transform";