Images in UMG are either texture2D or slate brushes.
If you need an array of widgets, I would create a new widget just for you image and call it say ImageWidget. Then in your main widget, do a “create widget” and choose ImageWidget. from there you can drag from the return value, with context sensitive unchecked, and do an “Add” from array and it will create the “Add” array node with the small array symbol preset to be an array of the ImageWidget.