Best software for face comparison in photos?

Hi everyone, does anyone know of a simple, free program for comparing faces in photos? I stumbled upon an old photo from 1929 showing a group of soldiers from the Kingdom of Yugoslavia—and there’s a chance one of them might actually be my grandfather. I’m hoping to compare that shot with the oldest known photo of him, which dates back to 1969. Even with that forty-year gap, I'd love to see if any facial recognition tools can help me figure out the probability that it's really him.

http://en.wikipedia.org/wiki/Facial_recognition_system

Doubtful you'll pull it off. Most likely it's just a group shot where everything's too blurry or tiny to actually compare anything. But hey, who knows...