For an animation a friend and myself were doing in class, we decided to make a rap video, involving everyone who was taking the comtech course this semester. We wanted different heads on different bodies, and orignally we were going to cut and paste using magazines, but quickly decided we could edit all the bodies on photoshop.
All the bodies and heads don't fit together perfectly, and we sort of wanted it that way, for comical value.

Step 1: What Programs to Use/Materials.

The only thing you'll really need for this, is photoshop, and your imagination!
Open photoshop, then open the photo of your choice.

Step 2: Unlock the Background Layer.

In the bottom right, you should see a little box, titled 'layers'
The current layer you're on should be titled 'background'
And should have a little locked icon near it.
by double clicking the layer, a window should appear in the middle of the screen. If you wish, you can put a new title on your layer,
where it says, 'Name:'
though all you have to do is press the 'OK' button.

Step 3: Lasso Tool

Now, you want the head selected by itself.
By clicking the 'magnetic lasso' tool-on the left side tool bar, it looks like a tied triangle with a magnet ontop of it.
Using the magnetic lasso tool, click a starting point on your image, and outline the area of what you'd like to use.
Because im changing heads and bodies, i outlined the head.

Step 4: The Body.

Open another window with your photo in it, do the same thing, though not with the body, with the background.
Using the lasso tool, highlight the background and proceed to cut it out.
(you can also use the magic wand tool for plain backgrounds, but that will be in a completly different instructable)

Step 5: Copy the Head.

Go back to your image of the head-which should still be highlighted by your lasso tool-
then to edit, and 'copy'
cut will work aswell, though i suggest copy, just incase you make a mistake!

Step 6: From Head to Body

Now that you've copied your head image, go to the image of the body you wish to use.
Again, go to edit, but this time, click paste.

Step 7: Sizing.

Your head should be now on the screen-though sometimes, the head image is to big to begin with, and wont appear directly on the picture-
though that is very easy to fix.
Click on 'edit'
then near the bottom, click on 'free transform'
This will make a grey outline apear around your photo.
You can re-scale and move your photo using that box.
I suggest re-scaling from the corners. I find it makes the picture more even, oposed to being too long, or too wide.
Once your picture is re-scaled, move it into place on the body.

Step 8: All Together.

Now, you may want to remove the head that was on the body, or remove more of the neck to make it look like it fit better.
By clicking on the layers on the side, you can select what you're editing.
if you click the layer with the head on it, you will only be able to edit the head.
As so with the body.
I just used the eraser tool to take out little things i didn't want,
but you could use the lasso tool, or the magic wand tool.

Step 9: Making the Head Just Right.

And thats how i did it!
Not to hard at all.
Hopefully this helped with anything you'd like to edit.
Later i will make an instructable on how to use the magic wand tool to edit.