Here's how to add images to a Presentation using the Images Section:
In the Presentation Editor open an existing Images Section or add a new one.
When the Section is clicked on, its settings box will expand on the left.
Click on the space next to "Background" and a new panel will appear, allowing you to upload an image or set a background color.
Click on "Upload Image" to select a file
After choosing the file, click Upload.
The image will be inserted and cropped to fit the "Aspect Ratio" which is controlled in the settings.
Remove or Replace Image
To remove the image or replace it with a new image, click on the thumbnail space to open the panel again.