Here's a super quick and nasty guide I chucked together to outline the steps I take: 1) Get a photo of someone you want to manipulate and once you have that, start looking through the stock photos and photography sections for a photo of an animal, but make sure that the lighting conditions and angle that the photo is taken at are similar in both photos. You may need to use more than one photo and take elements of each for different areas of the face/body. 2) Copy the animal's face onto the model's and lower the opacity of the layer 3) Use 'Free Transform' tool to resize and rotate the animal's face to fit the model's face better and use the liquify tool to make finer adjustments. 4) At this point you may want to duplicate the layer of the model and smooth out her face (essentially make her face flat as if they don't have a nose). The patch tool is handy for this, but simply using the eyedropper and painting in the face works just as well. 5) Change the blending option for the layer that has the animal face. You may want to use multiply to darken the face. You may find it useful to duplicate the animal layer and play around with different combinations of opacity and blending options. 6) Tidy up the picture, use the eraser tool to clean up any left over backgrounds from the animal photo. Use the dodge and burn tools to lighten and darken areas as required. Pay attention to lighting and add shadows and highlights as required. 7) You may need to paint in fur to make the image more consistent. I don't think I've had a single photomanip where I haven't had to paint in some fur. Start off with a base colour, and then add darker and lighter layers. I personally like to use different layers for each colour of fur that I add. To draw the fur, I just use the dune grass brush, though there are far better ones around if you just do a search here in dA. You may find it useful to set the brush to paint in the direction/angle of the mouse strokes (you can set this in the brush settings). 8) Paint the lips/eyes/ears/teeth on separate layers as required 9) If the colour/saturation in any part of your photomanipulation doesn't quite match up with other areas, use adjustment layers to get them blending in better with the other layers. This is usually necessary if you're working with several different photos.
I also recommend checking out the tutorial by as well [link]
Let me know how you go if you attempt it! I'd love to see the result