This forum does not have image storage capacity, you cannot upload images to it.
You can upload images to this forum by using the "Attachments and other options" while composing a message, and then attach an image. A test image follows attached (so it seems to work for me, at least: Snow leopard).
The attachments capability is not intended to become a photo upload server. you can upload 4 attachments or a maximum of 4mb of files, be they text or images. Images display @ 320 X 320, so its a back door way to quickly show a image or two, but linking from your server is better.
If a large number of images were uploaded, the feature might be shutoff or curtailed.