There are several sites available to check whether you opened the ports correctly on your router. If you are at the actual site where the DVR is located you can use Canyousee.org. Simply enter the port you check and it will do the rest.
If you are off site and would like to enter the WAN IP address of the router you want to check then I suggest you use. Yougetsignal.com and choose the port forwarding tester. This tester I believe only tests HTTP ports and TCP ports and not UDP ports.