Yes, you can add photos as attachments using the URLs.
Here is the example. I have using an online photo URL to link in ArcGIS Pro and ArcGIS Online.
Right-click the layer on the table of content and configure the popup (https://pro.arcgis.com/en/pro-app/latest/help/mapping/navigation/configure-pop-ups.htm)
Once you configured the Popups you can visualize the photographs.