You would need to grab the ID and the character from the URL in this case v and 73021329 and look it up on the API as per https://github.com/justintv/Twitch-API/blob/master/v3_resources/videos.md#get-videosid
Which results in: https://api.twitch.tv/kraken/videos/v73021329
And you can use the thumbnails from the response