We can sort online photo sharing into 2 main categories :
1) Web based
Web based online photo sharing is a centralized server application allowing end users to upload photos from their PC to the company servers. Photos are stored and published from the central servers to the end users who cannot get back and store the shared photos on their PC. This is a "one to many" process. Online photo sharing services, photoblogs services and photos printing services are all web based. Main players are Ofoto, Snapfish or Flickr.
2) Software
Softwares dedicated to online photo sharing are decentralized applications with direct connections (photos transfer) between 2 users . This is a peer-to-peer (P2P) application that enables end users to upload directly their photos from their PC to their peers' PC. No intermediary servers. Most of software applications feature a "simple P2P photo sharing" process (Pixpo, Photoleap) but PixVillage features "Real P2P photo sharing" which increases the global efficiency of the network.