Ah so that explains the weird emails i've been getting.
To clarify, the forum in question hotlinked an image from one of the blogs i own.
Anyone familiar with the internet will know what hotlinking/image theft is and being a fairly popular blog we get a lot of that.
So to stop people hotlinking out images we use a .htaccess file that redirects visitors to another image if they aren't accessing it from the blog homepage.
The image in question isnt very nice, the whole point of it is to get the webmaster in question to stop hotlinking
Here's some more info on hotlinking and htaccess for those not in the know.