Developer Doug Beaver reports that users have uploaded over 10 billion photos onto Facebook to date, making Facebook the largest online photo storage site — dominating popular photo sharing sites like flickr (two billion photos) and Photobucket (6.2 billion).

Between two and three Terabytes of photos are uploaded to Facebook daily, and around 15 billion photos are served each day. “Photo traffic now peaks at over 300,000 images served per second,” Beaver writes.

With the right profit model, Facebook’s photo hosting service — which hasn’t been heavily promoted, but which has apparently won critical mass — may serve as a profitable window of opportunity. AllFacebook claims that, despite its high-use figures, the application is among the few Facebook features that “rarely has significant [usability] issues.”

Rival MySpace is trying to monetize its own plethora of photos through a deal with HP that enables users to print photos or create customized items. Since its acquisition of PhotoBucket in 2007, it has sought various routes to profit from mass image uploading.