I use Hash Animation Master but you cold probably use any modeller which has the capability of loading an image as a background template. I have a generic head model. I load it along with the front-view photo of the subject. Tweak the mesh control points until it matches the main features of the photo, then same from the side (then the front again, then the side ...!). Export the model in a suitable format for Poser. Apply a UV map to the model using UVmapper. Make a texture using a version of the original front view photo on the UV map. Import the head model to Poser as a prop. Position it. Use the swap body part for prop function. The new head is now the Posette head. Apply the texture. The new head has a fixed expression at present, but you can go back to the original model, tweak it to a new expression (maybe using a different photo) and use it as a morph target for the new head in Poser.