Check out example codes for "youtube video image". It will help you in understanding the concepts better.

Code Example 1

<!-- thumbnail -->
https://img.youtube.com/vi/<insert-youtube-video-id-here>/mqdefault.jpg

<!-- Others -->
https://img.youtube.com/vi/<insert-youtube-video-id-here>/default.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/0.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/1.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/2.jpg
https://img.youtube.com/vi/<insert-youtube-video-id-here>/3.jpg

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