Motif comes with a custom template for the Image Slider block called "motif_image_slider". This is what is used in the Motif demo in the full height header on the home page.
This template sets the slide image as a background image on the slide positioned in the center of the slide and set to cover the whole slide. It then adds the title and caption to the slide centered both horizontally and vertically. If a link is added, the link is rendered as an overlay on the slide, so clicking anywhere on the slide takes you to the link's location.
Note: In order for this template to render properly, there must be a height set on the container of the image slider.