At the moment you have likely defined the dynamic image resources within the TP4 file (or code) using local/private IP addresses. In order to have the resources available via an external URL, you will need to either use a VPN connection or use port mapping within your router directed to the Axis video server.

You should then be able to update the TP4 file (or code) dynamic image resources to use the external URL and provided your router supports reverse lookup (to resolve its own WAN IP - most newer devices do), then you will be able to see the images whether you are connected to your local network or an external network.