You can use YouTube Data API to retrieve video thumbnails, caption, description, rating, statistics and more. With the YouTube Data API, you can add a variety of YouTube features to your application.
For the high quality version of the thumbnail use a url similar to this:
http://img.youtube.com/vi/<insert-youtube-video-id-here>/hqdefault.jpg
There is also a medium quality version of the thumbnail, using a url similar to the HQ:
http://img.youtube.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg
For the standard definition version of the thumbnail, use a url similar to this:
http://img.youtube.com/vi/<insert-youtube-video-id-here>/sddefault.jpg
For the maximum resolution version of the thumbnail use a url similar to this:
http://img.youtube.com/vi/<insert-youtube-video-id-here>/maxresdefault.jpg
Here’s the Official Google Documentation for Youtube API
https://developers.google.com/youtube/v3/docs/thumbnails
Here’s where I get my answer:
How do I get a YouTube video thumbnail from the YouTube API?