It took all of a minute after Google announced Glass for privacy concerns to come to the forefront, and since then, the company has worked hard to calm everyone's fears. While Google itself might not bundle software that has the potential to invade someone else's privacy, there's little to stop a third-party developer from filling that void.
Take NameTag, for example. This is a future mobile app that has the ability to scan someone's face, and then query a number of databases to find a match. Information about that person is then displayed. Clearly, though, someone is going to notice you getting in their face with your smartphone to scan them. That's where the discrete Google Glass shines.
With the NameTag Glass app, any Glass owner would be able to scan someone's face without them knowing, and even if some precautions are put into place, short of a fog horn going off when the picture is snapped, it's probably not going to be enough to notify that person. And, let's face it, this is meant to be discrete. The idea behind NameTag is that you can learn about people around you before actually meeting them.
The privacy risks that arise from such a solution are no doubt obvious. Picture, for example, standing in a crowd and scanning someone at random. As it turns out, that person is an online social butterfly, and without any effort, you can learn about where they ate last night, where they got their car repaired, and where they last took a vacation. It doesn't take much imagination to understand why simple information like this would be useful to a social engineer.
The company behind NameTag understands that Google took similar features out of Glass for a reason, but it believes that in time, the company will reconsider. "Google has announced that facial recognition will not yet be supported for Glass; undoubtedly due to pressure from privacy groups but FacialNetwork.com believes that by providing applications with such vast societal benefits, Google will eventually reconsider."
I'm not as confident about that as they are.