As a rule, said Holmes, the more bizarre a thing is the less mysterious it proves to be. It is your commonplace, featureless crimes which are really puzzling, just as a commonplace face is the most difficult to identify.
If you use Facebook - as I do - Facebook in all likelihood has a unique digital file of your face, one that can be as accurate as a fingerprint and that can be used to identify you in a photo of a large crowd.