To post a picture inside a thread instead of at the bottom, you need to click on the little paper clip icon above the message board.
The manage attachment menu will open as it does when you click it normally. After you have uploaded your picture, click on the paper click icon again. It will, this time, list what pictures you have uploaded.
. You can insert them one at a time or it will also give you an option to "insert all."
You might want to click on the "preview post" button to see if the pictures are arrange as you wish, you can move them around by cutting and pasting the "attach" part different places.