I used gimp to create this one (transparent background):
First cutout the model / remove what you do not want.
Then grayscale it.
(I cheated and started with a already grayscaled image)
Pallet the image to 4 colors (Image->Mode->Indexed..)
Then change it back to RBG (Image->Mode->RGB)
You now have a 4 colors only image
Copy it to a new layer and switch to that layer
Tools->Color Tools->Threshold and create the black area (in my case I transformed the two darkest colors to total black)
Remove everything besides black in this layer
Remove the white in the bottom layer if you want transparent background
Blur each layer individually, merge layers and resize to your need
