Currently, image content loaded into AGOL can only be permanently used in journal/story mapping applications if the image content is shared publicly. While privately-shared image content can be added to a journal/story map currently, after some time (approx. 1 month) the privately-shared image urls expire and the links to the image content in the journal/story map break.
Image content on AGOL should be allowed to be shared privately ie: within an organization with a static url, which would prevent these links from breaking and allow journal maps that leverage images to be privately shared/shared within an organization.
