The Popular Grunge Look
Heads Up!
This article is several years old now, and much has happened since then, so please keep that in mind while reading it.
Let me tell you: It's a very short trip.
Open your image (Pro tip: it doesn't have to be a portrait :D ) in Photoshop
Now make two duplicates of the background layer. Press CMD (mac) or CTRL (pc) + J twice, and your layer palette looks like this:
3 exact copies of the same layer.
Now select the layer in the middle. We need to desaturate that completely. You could either go to Image -> Adjustments -> Desaturate, og you could simply press CMD (mac) or CTRL (PC) + SHIFT + U
And now you have this
With the middle layer now desaturated, or black & white.
Now select the top layer, og go set the layer blend mode to OVERLAY
And you're done ... and have now achieved that popular grungy look
Merry Christmas
Niels Steinmeier
Niels is on Twitter as @steinmeier