[paxys]

Yes, it can scale. The ideal way to do it is to queue all the updates sent to their server and process them by spinning up extra VMs right when they are about to get the burst of traffic (easier to do since they themselves determine what that time is). That way they don't have to pay for resources to sit idle the rest of the day, and a slight delay (say, a few seconds) before the photos actually post and are visible to everyone is acceptable.