[mouhtasi]

While this can evade detection using full-facial classifiers, it's not difficult to detect individual facial features. If you can detect the eyes, nose, and mouth, and have them in a region in an orientation matching a face, you could assume that it's probably a face. While it is less efficient it's still a possibility.

[bartl]

>If you can detect the eyes, nose, and mouth, and have them in a region in an orientation matching a face, you could assume that it's probably a face.

Or a car.