The board has a few way to post images. There is an image icon (a photo of a tree) in the tool bar above your posts. You can add a URL (for an image that is already on line) or upload an image from your computer.
Your best bet if you want to post a large image file is to go to imageshack.us and upload the image there... then use the forum thumbnail code to post it here (instead of the icon above)...
Be careful posting large images. Not all readers/viewers will be able to see huge images so your best option is to post a thumbnail through imageshack.us and allow the user to select to see a big image.
Uploaded images are shrunk in size when uploaded to BAN.