My wife and I were married outdoors in a beautiful setting near Pt. Reyes along the California coast. We put disposable cameras on all the guest tables. I don't know what happened but we never got any of them back! So my advice is to attach a note asking to use up the film and return to a designated place at the reception or person.
We hired a photographer. But I have a lifelong friend who is a talented photographer, and he took many informal pictures during the wedding, and put them into a little book for us. Those are a treasure. They captured what it was like to be there that day. I didn't know he was going to do it and I didn't ever notice him taking photos. That little book means more to us than all the photos we planned for, by a huge amount.