You only need the basic trust level to post links to trusted websites such as YouTube, Twitch, Twitter and these forums.
I also found out the other day you don’t need TL3 to post card images from playhearthstone.com
TL3 means you can post links and images from other sites such as Vicious Syndicate, Imgur, eg: your own screenshots from Hearthstone.
https://us.forums.blizzard.com/en/hearthstone/t/new-forum-guide-syntax-and-features