“The idea behind this technique is simple: place the paper prototype of the mobile application inside the mobile device. This is achieved by adapting images of low-fidelity (paper) prototypes to display on a mobile device’s screen. This allows users to get closer to experiencing aspects of the mobile user experience that are absent with paper UI sketches alone…These mixed-fidelity prototypes share some important characteristics with paper prototyping. They are still relatively easy to create and discard. They also look “sketchy” and “unfinished,” which allows participants to provide feedback they otherwise might not have shared for fear of criticizing a design that appears to have many hours of work behind it.”

Link: Paper-in-Screen Prototyping (uxmag.com)