How to pull a video thumbnail jpg from YouTube

If you ever need to pull a thumbnail jpg directly from YouTube, you can use the following process. 

Here is the link. You need to edit the portion that says 'ID' in the middle of this link:
https://i.ytimg.com/vi/ID/maxresdefault.jpg
 
Here is an example video. Note the ID of this video is 'RFGn-pTlM6s'
https://www.youtube.com/watch?v=RFGn-pTlM6s
 
Here is the link to download this videos thumbnail:
https://i.ytimg.com/vi/RFGn-pTlM6s/maxresdefault.jpg