I love the picture idea. And what I love most about it is the fact that you email the pictures to your volunteers afterwards. You may do this as well, but, in these emails to volunteers, you could also link to the pics on your social channels and/or encourage the volunteers to share the pics with their own virtual networks. Keep that virtuous cycle of engagement and reach going as long as it can go.
Your idea is also an excellent example of how hard we try to squeeze everything we can out of a piece of content or new initiative. I actually think that is a effective and necessary approach for all nonprofit marketers to take when doing almost anything. For example, we recently sent out a survey to partner organizations asking them to rate our volunteer programs. Of course, we added a question to the survey asking the orgs what they liked most about working with us and a checkbox asking if we could share their answers publicly. So, not only did we get responses to a survey about how we can improve our services, we also got a bunch of quotes and testimonials that we could post on social and add to web conversion pages.