You have a database in the iPhone called Photos & Videos. You store all photos and videos in there.
Then you can open any number of apps -- photoshop, Camera, Photo Viewer, Mail, etc -- and act on those files. Any changes you make will be centrally reflected in all the other apps, since there's only one copy of the file.
In the primary app for any particular database, say Photos, you can create albums and organizational structures based specifically on that type of data: Albums for photos, for example.