Federico Viticci at Macstories writes about a very interesting change in Apple’s latest iPhoto 2.0 app for iPhone and iPad. In the first version of iPhoto for iOS, images you edit stay in iPhoto unless you explicitly share them back to the Camera Roll. This situation applies to other applications, too, due to the sandboxing security architecture that keeps apps separated in their own virtual workspaces.
iPhoto 2.0, however, manages to tunnel under the sandbox walls and updates edited photos in the Camera Roll without any additional export step. If you view the image in the Photos app and tap the Edit button, you can edit the original.
In another great move, you can now delete photos from the Camera Roll from within iPhoto: Tap the More button (which looks like an outlined ellipses … ) in the bottom-right corner and choose Delete. There’s also an option to hide a photo from view in iPhoto there.
Go read Federico’s article for more details. Currently this functionality doesn’t seem to be accessible by third-party developers, but I’m hoping it doesn’t stay Apple-only.