As I've mentioned before, my imageboard is a nasty little beta system, so I'm never sure if it's working or not. Do you see my avatar, or is there a little red X there instead?
Your webserver is set to disable hotlinking of images. If any request for the image is made where the referer field is not blank or set to your website, the server responds with a 403 Forbidden message.
On an Apache web server, the only two places I know of to place directives which would result in this behaviour would be in an .htaccess file inside that folder or one of its parents or inside Apache's httpd.conf. I have a feeling the answer will be the latter and that will be out of your control.
It may be possible to override this behaviour. Try placing a file named ".htaccess" in the same folder as your images with the following contents:
I've taken the .htaccess advice and have yet to see improvement. I'm also contacting the people that run the UK hosting site; maybe they're blocking it. Augh.