If you have a camera cell phone you can send photos to your broadcast via email.
You just need a phone that can send email (almost all can.) You set it up using the Mobile tool. The Quickstart Tutorial walks you through it, but the abbreviated version is: first, click on the "Email" tab and choose one of the rather odd-looking email addresses from the list; then add that address as a new contact in your cell phone's contact list. When you take a picture with your phone, follow its instructions and send it to the email address you just chose. That's it! In a minute or so the photo will appear in your broadcast.
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. You can title the column with either a graphic or another text box, such as "Uncle George's Vacation."
If the collaborator just wants to send in photos via email, have him or her send them as attachments to the special email address.