See this thread…
http://www.axisandallies.org/forums/index.php?topic=21305.0
…for the picture-posting procedure I copied below. I don’t know the minimum number of posts needed for the attachment feature to become available, but I think it’s around 10 to 15.
At the bottom of the posting screen, click “Additional Options…”. Use the “Browse” button next to the Attach window to find in your computer’s file directory the picture you want to load. Click on “(more attachments)” if you want to load more than one picture. Maximum attachment size allowed: 256 KB, per post: 3.