Google has added Panoramio photos to StreetView images.
Google’s image-matching algorithms will analyze them at some point to see if they are also a good match for a Street View location.
Google has offered images on Maps for some time, but not directly integrated into StreetView like this.
A thumbnail appears in the upper right of the StreetView image (see below). Clicking it opens a new view of the location with a horizontal scrolling bar of images. Users can click any of the images to enlarge. Google is implying it will only use a limited number of high-quality images for any location.
Here’s an example where the new user images do exist, for the Paris monument Arc de Triomphe: