Originally Posted by egentry

I found the button, but take a look at this picture.
<IMAGE SNIP>
Note that the button is a white image. When the background is light colored it is hard to see. If the app defaults to the back camera and you are holding your passport up against your white shirt, the button is invisible.
See how Apple handles this in their camera app
<IMAGE SNIP>They put a black background around the front/back camera button in the upper right hand corner.
A dark background around the button would make it a lot more visible.