Google adds user generated photos to Street View
Google is using geotagged photos contributed through Panoramio. The company also makes some of these photos available in other applications like Google Earth.
If you're viewing a location in Street View that has user photos available, an icon will pop up in the upper right corner of your screen letting you know that user images are available. When you click, a series of photos that you can scroll through will pop up. Just click the button on the right, which should now be labeled Street View, to go back to the normal view.