Often after the 30 days it still shows as exclusive and often I email again.
Why? You've followed their rules, if they can't stick to their own rules then that's their problem not yours.
True. But if someone were to see an image as exclusive and then see it elsewhere, they would assume I was at fault, even though I had already requested it to be taken off exclusive. It isn't worth any potential hassle and I just set a reminder on my calender for 30 days. It is annoying though that so many agencies set so many controls over our images. DT is way up there in the control freak league.
