Get the model to pose on the rock, fully clothed, and photograph her and the background. Then, paint the background, and, in the studio, get the model to pose naked in the same position (and with the same lighting) as she did in the photograph, enabling the artist to paint her posing naked on the rock.
There's also the possibility of creating an image in Photoshop or similar by combining photos of the naked model and the background, then painting that, but I think that might not provide as good results as using a live model. |