This is definitely CR infringement. Make no mistake about it. But it is also the sort of thing that happens quite often.
I can think of several ways this could still happen. One would be to post them in a part of the forum that was private and accessible only to members. Perhaps those with a hundred or more posts? Or maybe after they have made 20 posts, AND they've been members for a couple months? This would make it hard for anyone to get them that you don't want to find out about it.
Another would be to put them in PDFs or CBZ/CBR files (these are really just zipped and rarred collections of jpegs...they tend to be smaller, so many people prefer them who swap comic books online and such ) and upload the files to one of those sites that allows you to upload a set amount of material for free so others can get it. 100 MBs is the usual limit, and the files only stay up for a limited time before automatic deletion. I have not used them, however, and most are designed to be used by a few individuals with a set email address. You're supposed to include an email address for your intended recipient, and they receive the instructions on how to get the files. I don't know if such a system can be adapted to work within a forum, but it might be possible to post the download instructions here in the forum for everyone to use for the time limit. If the post could be deleted, or kept private, then it would be very difficult for anyone to find any proof that it is being done.
www.dropload.com is one example of a site that keeps files for up to 7 days. There used to be a number of these on the web, and they were all free. Dropload is only one.
Just a thought.
IsaacJ