Guerilla marketers interested in finding ways of gaining significant distribution for free on Facebook are increasingly exploiting a Facebook feature designed to make photos more social.

Photo tag spamming, as it could be called, is a tactic by which marketers who have built large networks of Facebook friends proceed to “tag” their friends in photos in which they do not exist. Why? Here’s how it works.

The Viral Dynamics of Photo Tagging

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