You might need to do URL to redirect your port. Some company provide DDNS as well as doing port redirect. It will be invisible to outside user. For example, your home IP cam is 202.112.113.14:8080, out side user will only type ipcam.selfip.com:80 or not (:80) ok.
Check here to learn more ... http://www.dyndns.com/support/kb/webhops_redirections.html