Bob's right it needs to be on line. If it's in the cruisemates gallery already all you have to do is copy and paste the address in the BB Code box. Then post it will post as a picture. If the picture is not on cruisemates then right click on the picture and get the location it should end in JPG like the address below.
Put that address into the picture box. This is the icon on your post menu
I hope that helps.