The skin of someone's face can be made to look dry or cracked with the right Photoshop effects. Isolate all of the face in the portrait, then hit "Shift," "Control" and "U" simultaneously to desaturate it. Create another layer, then find a close-up picture of cracked mud and paste that photo on that layer. Lower the opacity of the mud photo to match the desaturated portion of the face.
Select the icon at the bottom of the color palette to apply a layer mask, then set the blend mode to Color Burn. Once this has been done, darken the areas around the face so they don't look so different, and play with the RGB color palette until you find the look you want.