Flickr's most popular travel photos have also been linked to Yahoo's travel site.

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In addition, much of the content that people post on Tumblr from fashion and art to food and travel doesn't overlap with what's on Yahoo, which is strong in categories like sports, finance and news.

WSJ: Hazards of the Buzzy Startup in Light of Tumblr Buy

This traffic growth, however, requires a significant outlay in online brand marketing: Fees (principally through the purchase of travel-related keywords) to Internet search engines like Google ( GOOG) and Yahoo!

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