The Facebook Engineering team has just announced that Facebook users uploaded their 10 billionth photo to the site yesterday. Facebook is now serving over 15 billion photo images to users on a daily basis.

It’s an interesting stat as Facebook increases its lead as the biggest photo sharing site on the web. Even though Facebook photos are not very “high res” compared to other photo sharing sites like Flickr or Picasa, users continue to choose to upload their photos to Facebook because of how integrated Facebook’s Photos application is with the social graph. When users upload photos to Facebook, they usually “tag” their friends in photos, deeply associating photos with their friends’ Facebook identity.

This is a much more valuable social action than posting photos in an anonymous photo repository in some other part of the web. While other photo sharing sites will remain popular with different enthusiast communities, Facebook (and other social networks) will continue to be a much more powerful way to share photos of friends for years to come.