Here is a website for an organization who mission "is to further environmental and cultural conservation through ethical photography". They have a bunch of photographers but most notably is Art Wolfe (TV show: Travels to the Edge). They have concerns about "poaching to global warming, from habitat loss to cultural erosion, from sustainability to biological corridors, the work of conservation photographers covers the entire range of threats to biodiversity and is indeed a critical component in the conservation toolbox."
http://www.ilcp.com/ http://www.ilcp.com/?cid=22
I hope that might help you out in regards to photographers that shoot pictures that contain messages.