Depends on if the picture is already posted on an Internet server somewhere if so just click on the insert picture icon and paste in the URL (web address) of the picture.
Or you can create your own photo albums on garage journal...
On the menu go under The Forum - Quick Links - Your Profile and create a photo album and upload some pictures. Below each picture you will see a text box named "BB code" and all you have to do is copy/paste that code into your message posting to have your picture show up embedded in your posting.