Hmmm. A few years ago I was talking with a guy who worked on a system that pointed IR cameras at hands and did gesture recognition on them. They were doing use

Hmmm. A few years ago I was talking with a guy who worked on a system that pointed IR cameras at hands and did gesture recognition on them. They were doing user testing, and one of the folks they tried it out with happened to be a wiring contractor who was in the building at the time. It didn't recognize his hands; the IR cameras could not see them. Turns out that the lubricant he was using to pull cables through conduit was blinding them. I don't know what the lubricant was, but hopefully this reduces your search space dramatically :-)