Can't help if the MAC is any different, but I have to believe it is the same format on imgur.
I just click on the picture I want to transfer, then on the right side of the picture there are six blue option boxes. I left click on the box by "BBcode(message boards and forums)". Then go to your forum page, right click and paste and it should be there
Like this
Posts: 36 | Location: Michigan | Registered: 13 December 2011