Thank you @OP, if I may add:
First. You need jr.member rank or more
Or you can buy a copper membership from here:
https://bitcointalk.org/index.php?action=credit;promoteIn fact you don't have to create an account. You can upload images as a guest.
4: wait a minutes and f5 page
When the image is uploaded, you don't have to refresh the page just click the 3 dots button and copy the bbcode link.