Face Exchange - part 1

I'll start out with two pictures that I got from gettyimages (if you liked, you can go there and type "face" and browse through).
Observe that the girls are both facing forward, and both photos show the same resolution (important to make it natural).
We'll transfer the second girl's face into the first frame, creating a new layer.

To do that, let's resize the first picture. This is important because we want the second picture a little larger, so when we resize it, it doesn't lose quality. You'll see what I mean in a moment ^^
Go to Image>Image Size and make it a little smaller, like 95%.
Of course you won't need this step if the picture you are using is already smaller.

Now we're ready to do it. Select the Rectangular Marquee Tool, and copy it. Then, selecting the other picture's frame, create a new layer and paste it there.

To clean out the picture (we just want the face) you can either use the eraser tool or do it as I suggest.
With the Polygonal Lasso Tool, (this one below) select the face outline. It doesn't need to be perfect - mine isn't perfect =).

When you are done, you can go to Select>Inverse. It will invert the selection, and now we are selecting all the picture, but the face. Hit delete to have your picture cleaned.