If you host your pictures on a site like photobucket you can add as many photos as you like to a thread. It doesn't cost anything to join photobucket and you can keep all of your photos organized in different folders. When you want to post a picture, you click on the the little mountain icon above where you're typing, and a box will pop up asking where your photo is located? You have your photobucket account open in a different tab, and each photo will have a "direct link" address next to it. Copy and paste that address into the pop up box on FABO and hit enter. Your picture or pictures will be in that thread.
The reason you're limited to only one picture now is that every picture you add has to be uploaded to FABO's server which takes up space, which costs money. When you externally link your pictures, they are taking up space on Photobuckets server.
Hope this helps. I'm no computer expert, I'm just learning as I go!