Note: groups.io will be down for maintenance this evening, starting at 11pm Pacific Time (6am Tuesday 8/3/2020 UTC), for up to two hours.
I've made the following changes: For new photos uploaded, the thumbnails will be resized to a max of 2048 on their longest side. Previously it was 720. This is the image that is displayed in the single photo view. I also decreased the JPEG quality to 90, from 96.
Best I can tell, this is what Flickr does. Again, this will only apply to photos uploaded starting now.