Question

I use UIImagePickerControllerSourceTypeCamera in iOS. My purpose before using the camera is to guide the user to position the camera precisely in front of the image objects. I have a known target image (TI), a playing card, more specifically a 7 of Diamonds, and I need the 7 on the TI to be in the correct position in front of the camera. Is there a way to either superimpose on top of the screen the TI when the user is taking the picture, or to mask part of the screen so that only the place where the 7 appears will show the picture to be taken.

Once the camera is positioned correctly, I will ask the user to keep the camera still and position unknown cards in front of the camera without looking at the card.

Answer 1

The UIImagePickerController has an cameraOverlayView property to which you can assign an instance of a custom class. This class can draw the target area graphic that you need and it will appear on top of the camera image.

If you need to check that the card is actually within that area, then you are in a computer vision zone and things become much more complicated. OpenCV is a typical starting point for making sense of what a camera is displaying.

cameraOverlayView

The custom view to display on top of the default image picker
interface. @property (nonatomic, retain) UIView *cameraOverlayView
Discussion

You can use an overlay view to present a custom view hierarchy on top
of the default image picker interface. The image picker layers your
custom overlay view on top of the other image picker views and
positions it relative to the screen coordinates. If you have the
default camera controls set to be visible, incorporate transparency
into your view, or position it to avoid obscuring the underlying
content.