Here's another technique we like here in the workshop; try it if you're after a "dark comic" or "woodblock stamp" kind of effect for your digital photos...

The first thing you'll need for this technique is a good quality, high contrast image. I'm starting out with this one (from the stock.xchange):

Make a Duplicate of it (Image>Duplicate) so you don't potentially destroy the original, and then make a copy of the Background layer by pressing <Ctrl>+<J>.

 

Reset your default colors (Black & White) by pressing the <D> key on your keyboard, and run the Find Edges filter (Filters>Stylize>Find Edges). You should have something similar to this:

To get rid of the color and add a bit of a woodblock effect, run the Photocopy filter (Filters>Sketch>Photocopy) and adjust the filter to your liking. I used a Detail level of 14 and a Darkness setting of 2 for this image

:

To really define the black lines, make a Threshold Adjustment layer, and choose Multiply as this layer's blend mode (you can adjust the opacity of the Adjustment easily to add more or less of this effect).

This creates a pretty cool "woodblock" effect, like one of the old-timey wood cutouts from the Middle Ages:

 

To create a "Dark Comic book look", like one of the recent Batman graphic novels, click the Background copy layer created in the first step to make it active, and change its Blend mode to Soft Light:

 

As a final step, select the magic Wand tool (<W>), and change the settings in the tool properties bar to Tolerance:32, Anti-aliased ticked ON, Contiguous ticked OFF, and Use All Layers ticked ON. Single-click in the white area to create a selection.

Now choose the Threshold Adjustment layer, and create another Adjustment layer, this time choosing "Solid Color" as the type. Choose a color, and your mask will be already created:

To change the color, simply double-click the color panel in the layer thumbnail, and pick a new one - simple, huh?