An image processing apparatus which is capable of extracting embedded information from the back side of a printed document without causing degradation of reading efficiency. The synthesis filter circuit forms a filter by receiving coefficients from the coefficient calculating circuit. The free end of the door carries a latch member which engages an underside of the opposite side of the door frame when the door is partially or fully closed. An insulating material surrounds most of each of the nanostructure electrodes, and a region of the insulating material surface is functionalized to promote attachment of the selected species particles to the surface.