In the GDR2 update to Windows Phone 8, Microsoft had made an
important change to how the platform's camera capabilities work:
Now, you can choose which app opens when you press your
handset's Camera button. This change lets newer handsets like
the Lumia 1020 come preconfigured with better camera apps, but
it also lets any GDR2 user choose the app that works best for
them.  Note: I recently added some information about the GDR2
changes to Xbox Music in Windows Phone 8 to my free eBook, Paul
Thurrott's Windows Phone 8. This article represents an expansion
of that material.  While unexpected, this change follows a
familiar pattern of extensibility that exists throughout Windows
Phone. In previous versions of the platform, handset makers
could extend the built-in Camera app with their own settings
(including such things as scenes) and users could of course add
additional photo apps, including so-called Lens apps which
integrate directly into the built-in Camera app.  In GDR2,
Microsoft has taken the next logical