Welcome to the forum!
First you have to upload the photos. You can do it by re-opening your message by clicking the "EDIT" button.
Then, click "MANAGE ATTACHMENTS" to start attaching the photos. Make sure the photos meet the requirements to be uploaded (they have to be rather small size, but detailed information you wil find at the link below).
http://www.vikingsword.com/vb/showthread.php?t=13631