how do you copy pictures onto the boards

Doesn't posting the link show the picture?

https://pre00.deviantart.net/bd90/th/pre/f/2017/266/b/c/yasuo_01_by_sungben-dbodnpl.png

https://i.imgur.com/x5s9cMy.jpg

You do need to use imgur or something similiar to upload your picture to the internet first though...

https://boards.na.leagueoflegends.com/en/c/memes/auH9m6ea-posting-images-and-gifs-on-the-boards

That should help.