Tom Warren, writing for The Verge:
Instagram Windows Phone users can use the app to upload photos, but they'll need to shoot photos separately using the camera as there is no direct in-app camera support. A button within the app links out to the camera, and returns the photo after it's taken to apply a filter and upload it. Instagram says "as with every platform we take into account how users are using the platform natively, and thought this was the best approach."
To be fair, this version that is currently in the Windows Phone store is a 'beta', but for heaven's sakes why release an app that can't perform the primary function of the service? A few more weeks to create a fully baked version (even if it didn't have feature parity with the iOS and Android versions) would have been worth it. Windows Phone is three years late to the party, so waiting a bit longer to have a proper, elegant user experience would have been the correct choice.