This simple technique uses the same photo twice—next year’s Christmas card, possibly?
Here’s the original photo I used in my example.
Press Command-J (PC: Control-J) to duplicate the Background layer. Press Command-T (PC: Control-T) for Free Transform, and then hold down Option and Shift (PC: Alt and Shift) while you click-and-drag a corner handle to scale the copy down to the size you want. Don’t commit your transformation yet, though.
Step Two. ...