The name of this program is Gender Recognizer, but it says it attempts to recognize male/female faces. Quick lesson:
Gender: boy, girl, etc. (some cultures have more than two of these[0], and others do not identify with either of those two)
Sex: male and female
In other words, if your goal is to try to determine if someone is XX or XY, "gender" is not the word to use.
Regardless, I would tread lightly with this, because this could presumably be used on pictures of transsexuals and transgender people. Also, incorrect matches for something like this would be very not cool.