You'll need to upload the file to a site on the internet and then include the URL for the image in the "Optional Image URL:" text box at the bottom of the message post/reply page.
If you don't have a site, to which, you can upload, you may send it to me as an email attachment and I will upload it to the History-Sites.Com web server. Unfortunately, I am traveling this week, so it might take me a couple of days to get it online.
Jim Martin