Hi Jeanine -- Unfortunately there isn't a way to do that easily in our Story Map Builders at the moment, but you can do it using a Flickr gallery. See this article for more information.
Jeanine, I would think maybe you could make a looping video that showed these four pictures in a slideshow-like format and use that video as your media on the main stage and have it play automatically. Maybe. Or instead of a video, use a GIF creating program and create an animated GIF that would loop these images together.