It's better to make names of survey's image files case-sensitive within Survey123 Connect, this will make it behaves the same when images will be accessed through HTTP/HTTPS protocol after it's published, in format of https://<org_url>/sharing/rest/content/items/<item_id>/data.
When I created a survey with embedded image files, everything tested fine in Connect and images showing correctly. But after I published my survey and tried to access it through shared link, images couldn't be found just because of a case change in file names. It's can be quite confusing if we are seeing differently in Connect and through web survey, it took me sometime to find one old post which provided the hint and solved my issue: Solved: Showing or hiding repeats using conditional statem... - Esri Community
