There is a long-standing issue that allows us to see an image thumbnail in a companion app notification but won’t allow us to load the full size image. Using Media Browser is the preferred location to store images due to security reasons. The only alternative is to store images in the www folder which is open to the public internet when using Nabu Casa for remote access.
The issue is outlined in the following community post and github issue. While the issue is closed, the issue is not resolved.