Inside Facebook

New data shows Facebook’s lead in the photo sharing market has increased dramatically, both in the US and worldwide, in the last four months.

Erick Schonfeld has the latest charts from analytics company Comscore that show Facebook Photos growing by over 40% in the US in the last four months from 23.9 to 33.6 million unique visitors. During that same timeframe, #2 Photobucket grew by 7% to 22.8 million, Flickr grew by 12% to 21.9 million, and #4 Picasa fell to 8.1 million.

Globally, Facebook’s lead in Photos is even more dramatic. Facebook Photos saw over 153 million uniques in January, while #2 Flickr saw only 66.7 million.

How has Facebook Photos gained so much traffic during the last 4 months? Aside from Facebook’s rapid growth during the last few months, one key reason is Facebook’s redesigned profile, which has placed a Photos tab on every profile page. Photos are now very prominent both on profile pages and in the feeds.

In addition, the viral dynamics of photo tagging are simply very strong. As we wrote last November,

Photos are extremely popular inside Facebook: Facebook gives both significant visibility on the profile page and significant distribution in the News Feed to photo-related stories. The reason Facebook is the most popular photo sharing site on the web is not because its features are the best, but because its Photos application is very tightly integrated with the social graph.

Tagging is the primary means by which photos are made social: when a user uploads a photo, they can “tag” their friends who appear in the photo. Notifications are sent to tagged friends letting them know that a new tagged photo of them exists on Facebook, and feed stories are published on both the tagger’s and taggee’s profiles.

Users who receive a notification that they have just been tagged usually investigate the photo. If they don’t want to be associated with the picture, they “detag” themselves from it. Similarly, users who see a feed story about their friends being tagged in photos often check out the photo.

Bottom line: Photo-related notifications and feed stories both get a lot of impressions and have a high conversion rate inside Facebook.

As a result of the rise in popularity of Facebook Photos, some marketers have taken to photo tag spamming as an aggressive marketing tactic, while some Facebook Platform applications have used photo tags as a creative mechanism to spread the word about their applications.