Photography is a lovely thing. I can take a picture of my school, from one angle, and it will be my own work. Also, someone else can take a picture of my school, from the same angle, and it will be their work. Really, it depends on who clicked the button. Take this for example:
This is my shot,
and I totally reserve all rights Darn user contributions
I'll tell you right now, they are the same model (Airbus A330), same location (Amsterdam Schipol), same a lot of things. But the works are distinct, in that I took the shot on top, and someone else took a shot on the bottom.
When people apply licenses to their photographic work, it is normally only to their work, not the object that they took a picture of. Hence, if you were to open source the road, and I take a picture of the road, then the picture will be my work, and under full copyright.
Therefore, Google doesn't really need to do much. Many things that Google blurs out is for privacy reasons, if I walk beside a street view car, they'll have to blur out my face. So, if there is any issue, they simply blur it out.
The pictures that Google takes is their own work. Therefore, they are able to license/place a full copyright... etc. And because the photos belong to Google, they are able to do whatever they want, regardless of whether a similar shot has been taken.
Google is able to relicense these works because the photos belong to them. Since it is their own work, they are able to do whatever they would like with it.