I understand the Scratch team has only blocked images unless they were uploaded to a certain site. I would like to know how to do that, because I would like my forums to be as safe as possible. So, how would I go about doing that with FluxBB?

Somewhere in the regex for the BBCode you should check the website the image came from. I believe this must've been one of the lst changes to the 1.4 website code, you can try to find it..

Add it in the parser.php file.

Add what in.