Ahh, I deal with copyright issues on Graphics and Design often in my business.
It gets to be confusing etc. when you grant use of something, and in this case the copyright too.
I would just ask you this. Is it going to be worth it to Treasurenet to legally go after someone for the use of a photo that was on one of the forums. In practical terms, who will be keeping track of all the photos and looking for one published somewhere? In practical terms I would doubt the return would ever be worth the cost. And should that ever happen just ask yourself how many would keep posting photos on Tnet after something like that happened?
I don't think that is the intent of the agreement, and I just don't see where it would benefit Tnet to pursue something like that.
Just my two "wheat cents" worth.
MP