I had quite a discussion with one of the viewers regarding my video instruction how to download YouTube thumbnails.
You may remember that I suggested to add to this link where this is your YouTube video id the word hqdefault.jpg to get HQ thumbnail. The viewer told something about searching for og:image but was so poorly communicating that it actually took me 3 months to figure out what it was all about. It turns out, you can find the link to this image by searching the source code of the YouTube video page for og:image. This doesn’t deny but supplement my original video. Just add maxresdefault.jpg instead of hqdefault.jpg to the link for best quality image.