I agree. It seems this could be used to determine only whether the testee is not-human. It's trivial like you say, to trick the test into believing it is human

I agree. It seems this could be used to determine only whether the testee is not-human. It's trivial like you say, to trick the test into believing it is human by not finding a face. At first glance I thought the test was only to determine whether the testee is definitely not-human but the description actually implies categorising into computer and not-computer: "FADTCHA(FAce Detection Turing test to tell Computers and Humans Apart) is a type of challenge-response test to determine whether the response is generated by a computer. The test involves asking a testee to find* a face in a presented image and draw a square region of the face. If one correctly finds a face, it can be presumed that it is a computer, otherwise it will be regarded as a non-computer."