Slide’s Thumbnail
Set a thumbnail for the slide if your slider has thumbnail navigation, or just set a thumbnail to be used for the slide’s admin preview.
Thumbnail Dimensions
Choose From Slider Settings (recommended setting), or “Original Size”.
Thumbnail Admin Purpose
Set this to “On” to use the thumbnail as the slide’s admin preview. Or if set to “Off”, the slide’s admin preview thumb will be taken form the slide’s main background image.