A preview image on a video is like the cover on a book. It can provide some instant context to the viewer of what they're about to watch - far more than showing them a random page (or still frame).
Preview images in Stile - previously only available to the Content team - are now ready for everyone to enjoy. When a teacher uploads a video from their computer or tablet into a lesson, they can now customise it by uploading a custom preview image. This is entirely optional - if you don't upload an image then a still frame will be used automatically instead. Adding the preview image gives the video a clean, finished look and can work wonders in piquing a student's curiosity.
Learn how to add videos to your Stile lessons here.