Abstract: Discrete light sensitive exposed but undeveloped sheets which are stacked in a dark box are transferred toward or into one or more developing machines by one or more suction cups which can jointly attract a single sheet at a time or each of which can attract the uppermost sheet of one of two or more stacks of sheets in the dark box. A suction cup which attracts a portion of the uppermost sheet of a stack in the dark box is caused to flex the attracted portion above and away from the sheet below the uppermost sheet in order to promote separation of the uppermost sheet from the remainder of the stack. The flexed uppermost sheet is then at least partially extracted from the dark box and is monitored to ascertain whether or not its underside adheres to one or more sheets.