1) Create a new layer above your image layer and make sure the new layer is selected.
2) Select all (ctrl + a)
3) On the menu go to Select > Modify > Border, and specify how many pixels wide you want it (this may take a couple tries to get it the size you want as it depends on the size of your image and your ppi).
4) Make the forecolor the color you want your border to be
5) Fill your border (alt + backspace).
6) Deselect (ctrl + D)
I you want it to blend, you can do a Select > Feather after you modify border. I like to feather about half of my border size.
Jim Lunde
We all agree your theory is crazy, but is it crazy enough?