From the Instagram blog:
Today we’re announcing Layout from Instagram, a new app that lets you easily combine
multiple photos into a single image.
The app I was occasionally using for this purpose was last updated for iOS 6 so it’s good timing for me.
It makes sense to not put this inside the existing Instagram app – people are searching for a layout/photo arranging app anyway. Might as try and keep them inside the Instagram ecosystem rather than using a 3rd party app and hope they remember to post back to Instagram.