Modeling and recognizing landmarks at world-scale is a
useful yet challenging task. There exists no readily available
list of worldwide landmarks. Obtaining reliable visual
models for each landmark can also pose problems, and efficiency
is another challenge for such a large scale system.
This paper leverages the vast amount of multimedia data
on the web, the availability of an Internet image search
engine, and advances in object recognition and clustering
techniques, to address these issues. First, a comprehensive
list of landmarks is mined from two sources: (1) ∼20
million GPS-tagged photos and (2) online tour guide web
pages. Candidate images for each landmark are then obtained
from photo sharing websites or by querying an image
search engine. Second, landmark visual models are built by
pruning candidate images using efficient image matching
and unsupervised clustering techniques. Finally, the landmarks
and their visual models are validated by checking
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