If you look in the additional options menu below where you hit "sumbit reply" when posting. A window will pop up and give you the option of loading up to 5 pics at the time. They have to meet the requirements which are listed in the window.
A trick I use for people that have outlook is to copy the pic(s) you want to post and hit "email these items" it should ask you if you want to reduce the size click yes. Then when the email window pops up select all the pics and copy them to another folder. Then they fit just right on the board!