Turn any photo into a dot grid artwork with these Photoshop actions. You'll get great results with dots that change size. They get larger in brighter areas and smaller in darker areas. Free download available.
Now select Brush Tool (B), hit D on keyboard to bring colors to default and set your foreground brush color to black. Make sure all your brush options are set to 100% and then paint in the same layer, over the light spots to fill them up with black.
Now go to Select > Color Range and use the same settings as shown below. Press OK and then go to Layers Palette and turn off the visibility of the duplicated layer. Your screen should now look exactly like the second image below.
Select "model" layer and click on the Layer Mask button. Now you can just delete the "model copy" layer, as we won't be using it anymore. We needed it only for extraction.