Abstract: The present invention is used in photo-recording machines, such as microfiche recorders, which receive a document and record an image of the document on a photo-recording medium such as photoplastic film. The invention inhibits double exposures on frames of the film by use of distinctive indicator marks recorded on the film at preselected locations called indicator mark fields. The presence or absence of an indicator mark in such an indicator mark field signifies, respectively, that its corresponding frame is or is not available for recording a document image.In an improved recorder, prior to a proposed recording, a detector scans the indicator mark field corresponding to the frame selected for recording. If the detector detects an indicator mark, the recorder is inihibited from recording the document in the selected frame. A projection light source forms the image of the indicator mark field and projects it along an optical path in which a sensor of the detector is interposed.