To get a preview image for any video just add video ID to following URL:
https://cdn.viqeo.tv/preview/your video id.jpg

For example:
Video ID:  460f7e2f0a55541d918d

Preview Image URL:  https://cdn.viqeo.tv/preview/460f7e2f0a55541d918d.jpg

How to get video ID

To get video ID you can open 'Code' option in your feed and copy the value of data-vnd parameter.