There are probably 6000 ways to do this. I thought of a bunch of complicated ways using masks and curves, and levels and blending modes, and layer styles, etc. But then I thought of this. It seemed like the simplest way.
Copy the image into a new layer to preserve the original.
Use the Marquee Tool to make a rectangular selection of just the portrait. Get as close as you can to the edges without selecting any border.
Invert the selection so that only the border is selected.
Delete the border.
Now your layer has only the portrait surrounded by a transparent border.
Create a Solid Color layer and fill it with white.
Move it to just below the portrait with the transparent border.
There are lots of more sophisticated ways of doing this, but this way would take less than a minute.