Conceptual photography is always known and described as different things, such as an artistic movement, a working method or a historical tradition. Everyone has their own definition of conceptual art, for me, conceptual photography is always connected to photoshop. The picture you edited with photoshop will finally be something impossible but real.
Here I found three films on Youtube which are about a number of artists and critics of what they think of conceptual photography, and how they define it. They are Sean O'Hagan, John Roberts, Lucy Soutter, John Hilliard, Suzanne Mooney and Broomberg and Chanarin.