As per this ArcGIS Idea here: https://community.esri.com/ideas/15753-attachment-photo-viewer-widget-in-web-appbuilder
Please add a widget that lets you scroll through attachments for a featureclass. Similar to the details widget in Operations dashboard or the one trick attachment viewer templated app.
And please allow attachments (images) as dynamic content, e.g. to be used as teaser image in a list.
I have a feature service for bridges that includes both pictures of the bridges as well as PDF inspection reports. Ideal situation would be where I could select a feature, and a list of the associated attachments would be populated, with display options much like the list widget. Even a list where I could set it to display the fields I add about each attachment would be nice. Ability to click and open an attachment, also a plus. Ability to remove / add even better.