The process may look lengthy but it is simple to achieve by following these steps.
The tools icons are displayed in the accompanying photos.
I have also put extra information in the boxes on the accompanying photos, such as tool location/ and function (click on them to read).
Additionally, all of the tools mentioned can be found in the help section of Photoshop.
I am using Photoshop on a Mac but the principal of layers is the same for all photo editing software that has it.
Step 1: Step 1
The shots were;
1-The girls standing with her arm outstretched.
2-The girl with her hand holding her head.
These images were opened in Photoshop and I have labelled them in red for clarity of explanation.
Step 2: Step 2
After this step everything is a bit more fun.
Click on photo 1
press cmd + A (select all)
press cmd +C (copy)
Click on photo 3
press cmd + V (paste)
Click on photo 2
press cmd + A
press cmd +C
Click on photo 3
press cmd + V
You can now close photo 1 and photo 2.
The principal that we are now working on is that there is a background layer and that we have laid two layers over this; if we erase any of these upper two layers, we reveal the layer underneath; as if they were acetate sheets.
Now that is over and the fun begins.
In the layers palette that you see before you click on the eye icon adjacent to the thumbnail of photo 2; this will hide it while we attend to other things.
Click on layer 1 in the palette and using the eraser tool remove the girl's head.
Step 3: Step 3
Also, adding some white paint to simulate a cervical vertebrae is a classy touch.
Step 4: Step 4
Go to the lasso tool and select the magnetic lasso.
Use this to draw around the head and hand.
Step 5: Step 5
Press cmd + V
Click on the eye icon for layer 2. (this hides layer 2 which we will not use again; the head was pasted to layer 3)
This will reveal the head floating over the body.
Step 6: Step 6
Click on the move tool and move the head to a position where it looks as if it is being held by the outstretched arm.
Step 7: Step 7
Click onto layer 1 and, using the eraser tool, rub away the parts of the outstretched arm and hand that you do not wish to see.
The clone stamp tool can be used to extend the sleeve a little if needed. ( the clone stamp tool clones a selected area of your image and allows you to put that selection anywhere).
More detail on the clone stamp tool-
To use this you must first select the area you wish to clone from. To do this, alt + left click the area. Then you go to the area you wish to clone into, and left click to paint. You may need to redefine your points as you paint to achieve the best effect [simply alt + click on a different area])
Step 8: Step 8
I added some small white blobs to to simulate the light shining on the blood.
I used black paint to get rid of the redeye caused by the camera flash ( you will have to go back onto layer 3 if you need to do this).
Step 9: Step 9
Now there is only one layer to think about.
I decided to make a tighter composition by cropping the photograph.
Using the dodge tool ( on 15% opacity) I lightened some of the background to give a better contrast.
This is a perfectly good result but in the next steps I show how to get some variations on this photograph should you want to take the editing a stage further.
Step 10: Step 10
Push the saturate slider to -56 and the hue slider to +91 (play around for your desired effect)
As you can see an instant, undead complexion is achieved.
Step 11: Step 11
This looks like an old photo.
To make it look older use the eraser tool, on a soft brush and mid opacity, to erase around the edges of the photograph.
Then set the opacity to 100% and the brush size very low to make some scratches.
The brush to can be used to and some blobs of grey and black to give an aged effect.
It's hard to know when to stop . . .
Good luck and please contact me with any questions or suggestions that you may have.