I don't know if there's a way to specify the cookie domain in UBB. When I login to UBB, it sets "reaw3t_myid" and "reaw3t_mysess" cookies for the ".realtree.com" domain. If I log in with the "Remember Me" box checked, a "reaw3t_key" cookie is also set.
PhotoPost only recognizes me if I login to UBB with "Remember Me" checked.
Test Username: cdavis
Test Password: testing