1. A method for detecting overlapped flat objects in a sequence of flat objects, the flat objects having at least one of their edges exposed for viewing as they pass along a feed path, said method comprising: selecting a flat object in said feed path; capturing a digital image of said exposed edges of said selected flat object; processing at least a portion of said captured image encompassing said edges to determine a pixel density variation in a direction across said edges; analyzing said pixel density variation to identify maxima and minima in said variation, wherein a start of an edge is identified by a maximum and an end of an edge is identified by a minimum; and counting said maxima and minima to output an indication of a number of edges in said image.