Having pasted the definition, I'd argue that nowhere in the definition is there a qualification of how the effect is produced. It simply characterizes and effect, i.e a dark monotone outline against a light background. A silhouette is sometimes a shadow but not always, and a shadow is sometimes a silhouette but now always. But when it is both, then arguing that it is a shadow and not a silhouette is just silly.

That's like looking at a picture of Emiril and arguing "that's not a chef, that's a man".

I can achieve "silhouette" by drawing one, masking a photo, casting a shadow on a translucent screen, etc. Quibbling about the mechanism is silly.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)