i.ytimg.com/vi/_HYhAc_bPgk/hqdefault.jpg?sqp=-oaym

All about Thumbnail Images as ytimg maxresdefault especially in Search

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

thumbnail has different resolutions after subsequents API

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

Getting all the video thumbnails from a video

thumbnail grabber - Boing Boing

thumbnail grabber - Boing Boing