How to download Youtube Thumbnail ?

please let me know how i can download youtube thumbnail without any website ?

Code:

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https://$HOST/vi/$VIDEO_ID/$SIZE.jpg

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$HOST is one of

• i.ytimg.com
• img.youtube.com
• ytimg.googleusercontent.com

$VIDEO_ID is the video's 11-character identifier.

$SIZE is one of

• default
• hqdefault
• mqdefault
• sddefault
• maxresdefault

Not all sizes may be available.