An original work capable of copyright protection requires only "minimal creativity." Assuming that the silhouette is more than the most trivial drawing, it is protected by copyright. This further assumes that the author/publisher were able to discover your use.
Putting curly hair on the drawing creates a "derivative work," which requires a license from the author/publisher, and so is also copyright infringement.
Rather than trying to find a means to make the drawing work for you, and worry about being sued for infringement, you could simply find a friend, dress him or her up a bit like a classic lighthouse keeper (a hat, coat and some boots, is probably all you need). Then, take a picture of the person, put it in Photoshop, black it out, and you have your own silhouette.
A bit of a pain, but better than the alternative.
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