1. From the Stories view, tap the pencil icon for the story you would like to edit.
2. From the Storyboard, tap the large "+" button.
3. Tap to select the "Text & Image" page type.
4. Tap the layouts icon to change your layout.
5. Tap to select the layout of an image surrounded by a white border.
6. Optional: Tap the same layout multiple times to cycle through different background colors (white, off-white, light gray, dark gray, or black). Then tap done.
7. Tap anywhere on the image and then on the image icon to bring up the Media drawer.
8. Tap on an image to replace the default. Then tap "Done".
The images will fill either the height or width of the screen (depending on their aspect ratio) and will be surrounded by at least a 32 pt border.