This document discusses using reverse viewshed analysis to assess the location correctness of geotagged photos from Flickr. The researchers analyzed photos of two landmarks in Berlin - the Brandenburg Gate and Reichstag. They categorized each photo based on whether the geotag and label were correct based on the viewshed analysis and manual inspection. Their results showed geotags and labels were less accurate for photos further from the landmarks and users with fewer total photos. The researchers propose using additional data like observer height and a weighted credibility score to improve location correctness assessment of visually generated VGI.