Thanks for your comment. As a starting developer, I'm hungry for feedback.
By a "visual of the future shot" I mean that there is a fixed zoom-able picture in the app (it's an image of a flat facade of an old building rich in details) that shows you 1) the size of your background in meters (see "Background width" in the attached screenshot), 2) how blurred the background will be (both visually and in terms of the minimal detail that will be resolved at the background). So, it gives you a visual idea of the background, but not the background itself.
I was thinking at first about doing this with a user's pictures from the camera / gallery. But it makes things complicated as the user must specify the actual size of the image and make sure that there is no foreground/background, but only one huge surface.
More than that, for the range of the zoom that the app provides, it's not enough to use images even from my Phase One P40+ digital back ) So the app is working with a set of unified and aligned images ranging from super wide to super tele photo. It's difficult to expect from the user to prepare the set themselves.
So hope this answers your question and doesn't seem overly complicated.
Appreciate your opinion on this. Thanks!
PS I'm also curious if I should develop the same app for iPhone/iPad