A common workflow with collection apps is to capture photos of documents, IDs etc. Something that would improve the overall quality of these captures from field crews is a translucent overlay of the document's shape so users can align it correctly.
My suggestion is to add a new "appearance" type for photos named "rear-overlay". When a question has this appearance the photo must be taken with the device's rear camera and the viewfinder will have an image overlaid to guide the user. The image can be a SVG or PNG file that's stored and referenced the same way that "image-map" choice questions are. In addition, the question can have the image scale (0-100%), image anchor (top-left, bottom-right, center etc.), image rotation and overall transparency changed in the extended settings.