When composing your post use this icon...
When you click that icon (it's at the top of the composition window), a pop up will appear allowing you to insert the address or "URL" of your image. The "URL" or address is from Photobucket or Dropbox.
Once you do that something like this should appear in your message:
HTML Code:
[IMG]http://i1002.photobucket.com/albums/af144/muzanji/D95CAA83-4A76-4070-9FFB-7CBFCD9141D5-6813-000005EFD03AE5DD.jpg[/IMG]