1. A device comprising: an imaging subsystem, capable of providing image data representative of light incident on said imaging subsystem; one or more memory components, comprising at least a buffering memory component operatively enabled for temporarily storing the image data; and one or more processors, enabled for: receiving the image data from at least a first memory component among the one or more memory components; attempting to identify linear features defining a candidate quadrilateral form in the image data; and providing user-perceptible hints via one or more output components for guiding a user to alter positioning of the device to enhance a capability for identifying the linear features defining a candidate quadrilateral form in the image data; in which the one or more output components comprise a preview monitor enabled for displaying a preview image based on the image data, and in which the one or more processors are further enabled for providing the user-perceptible hints as hint icons displayed on the preview image; the one or more processors are further enabled such that attempting to identify linear features defining a candidate quadrilateral form in the image data comprises: generating a reduced resolution frame based on an input frame of the image data, the reduced resolution frame comprising fewer pixels than the input frame, in which a pixel in the reduced resolution frame combines information from two or more pixels in the input frame; displaying the reduced resolution frame on the monitor as the preview image; and attempting to identify the linear features defining a candidate quadrilateral form in the reduced resolution frame.