YouTube Thumbnail Image URLs

120x90 (has black bars)

https://img.youtube.com/vi/YOUTUBEVIDEOID/default.jpg

480x360 (has black bars)

https://img.youtube.com/vi/YOUTUBEVIDEOID/hqdefault.jpg

320x180

https://img.youtube.com/vi/YOUTUBEVIDEOID/mqdefault.jpg

640x480 (has black bars)

https://img.youtube.com/vi/YOUTUBEVIDEOID/sddefault.jpg

1920x1080

https://img.youtube.com/vi/YOUTUBEVIDEOID/maxresdefault.jpg