Despite traveling, I've been working on some things for #GoActivityPub and one of them is the ability to generate web optimized images when uploading JPG/PNG files.
The end result is an Image object containing multiple URL entries to small/medium web-optimized copies, plus the original.
This still requires some work on the frontend web components to be able to select from multiple variants based on the reported width/height.
But it also allowed me to fix issues with the ability of the library to process activities that contain multiple Objects.