Images can be added to each Course for use in Tile layout or for thumbnail images in Classic layout. They can be uploaded by going into the Settings sub-tab of the course and selecting "Choose File" in the Course Image section.
Note: Tiles are only available on the learner side. See this article to change your theme.
Note: All tiles in tile view are 250px x 250px and will be stretched to fit the tile. Images smaller than 250px x 250px will be tiled.