In the bottom right of the "Quick Reply" window you should see a button for "switch to full reply screen". Press that. In the new window you should see a button for "File Manager". Press that, then browse to your pic and follow the instructions to post it. Max picture size is not all that huge, and you need to format it in one of the approved styles (jpeg etc.)
The feature does not seem to be working right now, hopefully it will be working again soon.
