The Projected Interfaces architecture enables bi-directional user interaction with smart tangible objects. Smart objects function as both input and output devices simultaneously by cooperating with projector-camera systems to achieve a projected display on their surfaces. Tangible manipulation of the object and camera-based tracking allow interaction directly with the projected display. Such hybrid interfaces benefit both from the flexibility offered by the GUI and the intuitiveness of TUI. In this paper we present the theory behind how to consider interaction for projected interfaces with an architecture design and a proof of concept implementation using an augmented photograph album.