A signal processor includes a buffer memory for storing the image signal for output as a main image signal; a point setting section for storing a position on a temporal axis of the main image signal as a registration point in response to a given capture command, the main image signal corresponding to the capture command; a playback control section for causing the buffer memory to output an image frame following the registration point in response to a given playback command; a video capture section for generating a registration image based on at least one image frame in a neighborhood of the registration point of the main image signal outputted from the buffer memory, and storing the registration image; and an image superimposing section for superimposing the registration image onto the main image signal for display in a signal screen to generate a composite image signal.