i.ytimg.com/vi/F6Yx1_0GTT4/hqdefault.jpg

All about Thumbnail Images as ytimg maxresdefault especially in Search

Getting all the video thumbnails from a video

php - How do I get a video thumbnail from the API? - Stack Overflow

Video Thumbnail Viewer and Download

Download Thumbnail – Thumbnail Downloader

php - How do I get a video thumbnail from the API? - Stack Overflow