Google Street View has a new option to show photos uploaded to the Google-owned Panoramio. "Now you can browse user-contributed photos that have been precisely-matched to Street View images. Gorgeous photos from Panoramio allow you to see some of the world's most famous landmarks at an even closer level," explains Google.
Whenever you visit in Street View a location that has user-contributed photos, you can click on one of the photos for a different perspective. You'll find many Panoramio photos for popular places like Tour Eiffel, Duomo di Milano or Times Square.