Source: http://shutterstock.7eer.net/c/77643/108110/1305?u=http%3A%2F%2Fwww.shutterstock.com%2Fpic-112773976%2Fstock-photo-view-of-the-center-of-barcelona-spain.html

Not citing the source of photos, or using copyrighted photos, is plagiarism. Here is a post on why this is bad, and here is how easy it is to find allowed photos.