RealtyCam works with both photos taken by RealtyCam and with existing photos. To bring in existing photos, do the following:
Create a new collection by tapping the + button at the bottom of the main screen.
Tap the "Start from Photos" option.
Select the photos you'd like to import, in the desired order, and tap "Add".
That's it! Note that the collection is automatically named with the address of the first photo.
Here is a video of this process: