It’s the same deal with all of Blizzard’s forums, i.e. in order to embed pictures and/or post clickable URLs (to domains not on the designated whitelist of allowable domains such as Blizzard’s own websites) posters require Trust Level 3 in Discourse (the back-end software the forums operate on). Without that, you have to post pre-formatted text, as demonstrated here…
If you click your little avatar at the top-right of the forum, you’ll see a list of recent posts / replies, and down the right of that list are a number of icons. At the bottom, there’s one that looks like a little head and torso. If you click that, you’re taken to your forum profile, that shows stuff like how many days you’ve visited, the number of threads / posts you’ve made / read, the number of likes you’ve given / received, and the number of solutions (these only happen if someone marks your reply in Technical Support as being how their query was solved). At the top of that, it’ll say your Trust Level.
Regular = Trust Level 3
Member = Trust Level 2
(I can’t remember what Trust Level 1 is called).