You can collaborate on a broadcast in a number of ways. The easiest is just to add a text or mobile box for your collaborator, click on the Email tab, choose one of the email addresses, and then just provide it to your collaborator. Any time he or she emails something to that address, it will be added to your broadcast.
To save your changes when you close the window, just remember to click "Add Article."
If your collaborator just wants to send in photos via email, have him or her send the photos as attachments to the PNN email address you assigned.