I built on Kyle McDonald and Arturo Castro's face substitution work by creating a simple mesh editor. This lets you tweak how the texture is applied to your face so you can use images where the face isn't detected properly. It also means you can swap your face out for non-faces.
This video demonstrates the mesh editor with faces of The Joker, a skull, the fresco restoration fail, and a Guy Fawkes mask.
Source code for the mesh editor.
Jason Saragih's FaceTracker library
Kyle McDonald's ofxFaceTracker addon
Kyle's face substitution demo