The idea is that you can only access the pictures if everyone of the group is physically present. Sort of how multiple people need to turn a key at the same time to launch a nuclear missile.
Does installing this app somehow disable the regular camera app? Not sure how it ensures anything.
Joe takes a picture. I want to see it. But, oops, Billy isn't here to complete the nuclear launch procedure. So I turn to Joe and say "hey, text me that funny picture of Billy." What happens next?
Well, probably the photo is supposed to be taken with the Hangover app in the first place. I don't know app development, but does an app that accesses the camera _have_ to store the photo alongside photos taken with the normal camera app?
My impression was: group of friends are in vegas having a "Hangover (the movie)" style night and agree to only take photos with this app. That way, come the morning they can all review them, but only when they're all together.
Obviously, if they take photos with their normal camera, or if all apps have to save photos to the filesystem and can be seen by the built in photogallery app, this doesn't work. Maybe the app uploads them to the Hangover site and then automatically deletes them from the phone?