A device and a method for monitoring a plane in space over an interval of time to create an image representing the time history of the plane in space. A line image sensor (2) captures a series of line images of the plane in space which are converted to digital information by an A/D converter (4) for storage in solid state memory (3). The line image sensor (2) and the storage memory (3) are coupled for synchronous operation so as to maximise the operation rate of the line monitoring system and provide a single means for adjusting the operating rate of the line monitoring system. The series of line images are corrected for perspective distortion. To produce a time history image of the plane in space, the line images can be retrieved from the solid state memory (3) by a computer (7). The computer (7) displays the series of line images adjacent to each other to create the time history image. The present invention has a number of applications, including photo finish cameras.