Apple recently made a small but important, change to how screenshots are handled at the App Store to stop scammers. You used to be able to change the screenshots that show what your app looks like at any time. Duplicitous developers would submit their app with actual screenshots from their app, and then switch them with screenshots from other apps once they got onto the App Store.
Beginning January 9, app screenshots will be locked in iTunes Connect once your app has been approved. New screenshots may be uploaded when you submit a binary for an update to an existing app or a new app. For more information on capturing and using screenshots, read the Xcode User Guide.
Now developers will only be able to change the screenshots when they update the app, and can’t do it whenever they want to. This change guarantees that the screenshots Apple sees when they approve the app will be the screenshots you see when you’re deciding whether to purchase the app.
Even though the fake apps were removed once discovered and money refunded, it didn’t make the App Store a safe place to buy apps if you couldn’t entirely trust the validity of what you were buying. This change will help restore that trust from both consumers and the developers whose apps were being used in a fraudulent way.
Source [Apple Developer]