Warning: Enable attachments on a feature class can cost you some storage credit pay to ESRI, depends on whether you use ESRI server (arcgis online) or use your own enterprise portal server.
Old way to manage picture is to upload all your image to flickr.com or your own web server.
Then you save the image URL in attribute table.
For example:
San Luis Obispo, Laguna Lake Memorial Trees
https://slocity.maps.arcgis.com/apps/Solutions/s2.html?appid=a669ef38d0e7485fa77d5d47a669c5c8
Tree layer was used
https://services.arcgis.com/yygmGNIVQrHqSELP/arcgis/rest/services/LaguanLakeMemorialTrees/FeatureServer/0?f=html
Picture Image URL saved in attribute table
https://transparentgov.net/json2tree/datahub.io/embed/featurelayer_htmlpopup.html?backgroundlayerurl=https%3A%2F%2Fservices.arcgis.com%2FyygmGNIVQrHqSELP%2Farcgis%2Frest%2Fservices%2FLaguanLakeMemorialTrees%2FFeatureServer%2F0&layer=LLCTtrees&clickorhover=click
https://transparentgov.net/json2tree/esri/server/folder.html?org=https%3A%2F%2Fservices.arcgis.com%2FyygmGNIVQrHqSELP%2Farcgis%2Frest%2Fservices&url=https%3A%2F%2Fservices.arcgis.com%2FyygmGNIVQrHqSELP%2Farcgis%2Frest%2Fservices&arcgis_online_token=&select_folder=103&select_layer=0
story map upload all you image, picture to the same ArcgisServer along with your layers.
You don't need flickr.com, you don't need extra web server to save your image, All your image is in the same Arcgis Server.
Most important, you don't need bother youself to update layer attribute table to add image URL field, to save it. This is time consuming job, also hard to update, hard to manage, easy to make mistake.
Why not just use story map, forget all those trouble, ESRI will take care of everything about your image for you at a cost of paying ESRI storage (credit) with enable attachments.
Check these story map sample at here
https://transparentgov.net/cleargov1/1737/san-luis-obispo-ca-gis-asset-story-map