You understand correctly. Images that are stored locally on your hub are accessible from your local network, but not from outside this same network.
To have images that are accessible on and off your LAN, you will need to store them in a location that is available from anywhere on the web, and link to them.
You make a good point. I suppose they could likely and somehow allow images to be transferred through the Amazon Web Services (AWS) as well as the rest of the data, but that would likely require quite a bit more bandwidth.
That said, since it is possible to instead save those images on a web accessible location, would there really be value in doing this?
I also never really understood why if the image is in file manager it didn't display when you are not on your network. However I will add that every dashboard integration I have used handles images the same way, requiring a hosted image.
More reliable/centralized data access. Less moving pieces means you canโt accidentally delete an image from say your Google drive folder, or if the sharing protocol changes, youโre not having to update image links.
Speed and local control. If you are on the LAN, the images will load quicker. If the internet goes down, the images still load.