You can add multiple images in a source using the Image Slideshow plugin.
To do this, simply click Add Source > General Widgets > Image Slideshow…
Then click Add and choose the images you want to use.
You can also choose the transition you want to use; how you want it to loop; and how long you want the interval between images to be. When you are done, click Ok to save it.
Learn more about the Image Slideshow plugin here.