Do like this:
Hit the blue "Post Reply" button below the last post in this thread instead of typing up your reply in the grey quick reply box at the bottom.
On the screen that pop ups youl can find a grey button labeled "Browse" (or "Bläddra" on my Swedish system
).
Hit that one and select the file you would like to upload. One attached file per message is the limit.
If you already have the pictures online somewhere else you could use the button labeled "IMG" on the reply page to insert as many as you'd like in a message.
Happy posting
/Tiny Tutorial