External images should be thumbnail-resized by the MN server
This applies for e.g. to avatars, profile background pictures, and all community/collection/resource images. For the resizing, the client should be able to specify the size as part of the GraphQL request parameters.
And this tutorial about making thumbnails: https://www.poeticoding.com/creating-thumbnails-of-uploaded-images-and-pdf-in-phoenix
Antonis sez: "Being tracked by https://gitlab.com/moodlenet/servers/federated/merge_requests/51 along with general file uploads."