We currently do not support automatically adding photos to your story from a layer of features that were collected outside of our app builders. When you collect data from Collector or a similar application, you are uploading full quality images that can be 2-4mb (or more) per image. Loading all the images in a public facing web application would cause very long load times especially on lower bandwidth connections. Our team strives to provide a good experience for all users so we have not added this capability yet.
When you upload photos through the Story Map builders we automatically optimize photos for the web so they will load quickly on all devices. We are currently working with both the feature service team and the ArcGIS Online team to provide our apps optimized photos from so we can easily integrate other workflows into our apps. We do not yet have a timeline on when this feature will be released.
