Thanks deni.

I wouldn't know. I don't really know anything about
PhotoShop yet..

It's easy. Go to Resize canvas, and resize with a few
pixels. Then pick the bucket fill, and fill the white spaces
which were created after the canvas resize. But you can also
grab the foreground color to be black, so you won't need to
play with photobucket. ;D This is the easiest way I know,
and the one I use. If you don't get it, then use a brush and
draw manually your own border.