To better explain what I'm looking for, let's go back to this example picture...
I would take that image, eliminate the dress, because that wouldn't look right in a silhouette, it would appear that she had spikes or something sticking out of her side, then cut the outline of her body and a square rectangle of wood that would actually still be connected to her feet.
I then make a base, cut a slot in the surface, and insert the rectangle in the slot, so it appears she is standing on the base.
It's a very simple process and the silhouettes on a window ledge look quite nice.
Sometimes I make them out of metal, but for the most part I stick with wood.
Here's another example of silhouette-type art so you have a better idea what I'm doing.