To start off, open the image you want to edit (be sure to make a back up of it first, we dont want to lose the original)

Here is mine. if you want to use this image, you can downloadit HERE

Press "D" to reset your color palette back to black and white.

Now go to Image->Canvas Size.

For the width and height, add 30 pixels to the current size. so here is my current size

so i'll add 30 to the width: = 388, and for height = 413. What we are doing here is making the canvas bigger than the current image, hence, enough room for the border.

for the Anchor section (above image), leave it at default (center square selected), then click OK.

Now I have a white border

Now use your rectangle selection tool and make a selection of your image, about 10 - 20 pixels smaller than the actual image. see below.

Now go to Select->Inverse to inverse your selection. Now what you got selected is the outer border of the image.
Now go to Select->Feather and enter 4. This will soften the edges.

Now it's time to add some cool edging effects.

Go to Filter->Sketch->Torn Edges.

Now what you enter here is totally up to you. I set mine at: Image balance: 50, Smoothness: 5, Contrast: 20, and here's what I got:

You can play around with OTHER filters to get different edging effects, here are a few:

Filter->Distort->Ocean Ripple

Filter->Sketch ->Chalk &Charcoal

Well, that's it for this tutorial, experiment with the filters, maybe combine a few different filters to get some awesome borders.