"Using that information I created a trigger that only activated Darth Vader when someone with that avatar was playing (well, almost, anyone with that hair, glasses and smile, couldn't be sure about skin tone or hair color from the screenshot)."
Presumably the avatars are built by combining pre-made features.
Exactly. Each avatar is made up of 6 features, hair, hair color, skin color, eyes and mouth. No nose, because who needs them! So each part has a code, and I can store a face as a simple 6 character string. Then I just compared against the ids of the eyes, hair and smile. I actually allowed any glasses and any smile because I wasn't absolutely sure which one he'd used :)
Presumably the avatars are built by combining pre-made features.